If you are grappled and you attempt to cast a quickened spell do you have to make the concentration check to successfully cast the spell?
Nothing says you don't have to... and the rules state when casting a spell you have too but I understand what you are asking and why.
Quicken spell does not provoke an AoO and therefore no concentration check is needed if you are in melee range and want to cast a quicken spell.
Grapple states you need to make a concentration check to cast a spell.
I think that is where the confusion comes from. So yes, if you are grappled, you need to make a concentration check to cast a quickened spell.
Funkytrip:
completely true!
Quicken spell does not provoke an AoO and therefore no concentration check is needed if you are in melee range and want to cast a quicken spell.
Grapple states you need to make a concentration check to cast a spell.
I think that is where the confusion comes from. So yes, if you are grappled, you need to make a concentration check to cast a quickened spell.
Since this was well within the parameters that the OP posted I answered as I did -- which is to say exactly what you answered only worded differently and not quite as clearly since the situation was explained by the OP already.