Can you Counter a Counter spell?

[Yonman]

Say an opponent is using dispel magic to counter your spell and another party member has a readied action to counter, can he counter the opponents dispel magic spell used to counter your spell?

[Pizza Lord]

Yes. If your ally has access to dispel magic (or an ability that lets him counter with a different spell, such as Improved Counterspell).

Magic > Counterspell wrote:

It is possible to cast any spell as a counterspell. By doing so, you are using the spell’s energy to disrupt the casting of the same spell by another character. Counterspelling works even if one spell is divine and the other arcane.

How Counterspells Work
To use a counterspell, you must select an opponent as the target of the counterspell. You do this by choosing to ready an action. In doing so, you elect to wait to complete your action until your opponent tries to cast a spell. You may still move at your normal speed, since ready is a standard action.

If the target of your counterspell tries to cast a spell, make a Spellcraft check (DC 15 + the spell’s level). This check is a free action. If the check succeeds, you correctly identify the opponent’s spell and can attempt to counter it. If the check fails, you can’t do either of these things.

To complete the action, you must then cast an appropriate spell. As a general rule, a spell can only counter itself. If you are able to cast the same spell and you have it prepared (or have a slot of the appropriate level available), you cast it, creating a counterspell effect. If the target is within range, both spells automatically negate each other with no other results.

Casting a counterspell is casting the spell that will be used as a counter.

[Mysterious Stranger]

You could then have another character use dispel magic to counter the countering spell. This can continue until no more casters with dispel magic remain.

[AwesomenessDog]

I cast flusterstorm, wait wrong game...

[Pizza Lord]

I cast wet surprise! Wait, also the wrong game...

Interestingly, only the opponent using the first dispel magic to counter needs to make a check to succeed (moot point, since his is countered), since everyone else is using the same spell to counter the dispel magic.

[Azothath]

Yonman wrote:

Say an opponent is using dispel magic to counter your spell and another party member has a readied action to counter, can he counter the opponents dispel magic spell used to counter your spell?

Dispel Magic:A3 ...You choose to use dispel magic in one of two ways: a targeted dispel or a counterspell.

Magic Basics - Counterspell:

It is possible to cast any spell as a counterspell. By doing so, you are using the spell’s energy to disrupt the casting of the same spell by another character. Counterspelling works even if one spell is divine and the other arcane.

How Counterspells Work
To use a counterspell, you must select an opponent as the target of the counterspell. You do this by choosing to ready an action. In doing so, you elect to wait to complete your action until your opponent tries to cast a spell. You may still move at your normal speed, since ready is a standard action.

If the target of your counterspell tries to cast a spell, make a Spellcraft check (DC 15 + the spell’s level). This check is a free action. If the check succeeds, you correctly identify the opponent’s spell and can attempt to counter it. If the check fails, you can’t do either of these things.

To complete the action, you must then cast an appropriate spell. As a general rule, a spell can only counter itself. If you are able to cast the same spell and you have it prepared (or have a slot of the appropriate level available), you cast it, creating a counterspell effect. If the target is within range, both spells automatically negate each other with no other results.

Counterspelling Metamagic Spells
Metamagic feats are not taken into account when determining whether a spell can be countered.

Specific Exceptions
Some spells can counter other specific spells, often those with diametrically opposed effects.

Dispel Magic as a Counterspell
You can usually use dispel magic to counterspell another spell being cast without needing to identify the spell being cast. Dispel magic doesn’t always work as a counterspell (see the spell description).

Caster Level
A spell’s power often depends on its caster level, which for most spellcasting characters is equal to her class level in the class she’s using to cast the spell.

You can cast a spell at a lower caster level than normal, but the caster level you choose must be high enough for you to cast the spell in question, and all level-dependent features must be based on the same caster level.

In the event that a class feature or other special ability provides an adjustment to your caster level, that adjustment applies not only to effects based on caster level (such as range, duration, and damage dealt), but also to your caster level check to overcome your target’s spell resistance and to the caster level used in dispel checks (both the dispel check and the DC of the check).
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 note that Dispel Magic counters Dispel Magic...

Advice
like readied actions it is all pretty ineffective unless there are specific circumstances. It is better to be active & proactive than reactive. It is good to shut down an offensive wand (like enervation), removing protective spells on vulnerable foes, or removing ailments from allies.
In your example A & B prep a ready, C casts a spell, A activates his readied Dispel Magic to counter C, B has a ready to counter and pretty much has to counter A's casting as otherwise he'll lose the ready. So sure, it's possible. The question is who memorized all those Dispel Magics and why?

Why not try better tactics like have A do his ready. B casts something moderate like Obscuring Mist that A can try to dispel (just waste/absorb A's spell) or suffer not seeing B & C and losing the ability to counter. C answers with a fireball on A & his party. Then A can ready again (cause he's a dingbat). B & C can pummel A's group with fireballs and move or again cast a mild sensory debilitating spell and a fireball and move. Unconscious casters tend not to cast spells. Vanish, Invisibility, Illusion of Calm are all good counters to counterspelling.