The source of this problem is not as simple as it seems.  There is not a "maximum" parameter set in the code that restricts the number of coins that can be sent in one transaction but rather there is a limit on the size of the data that one transaction can consist of (block size).  Whats likely happening here is that your coins have too many inputs and the transaction gets bloated because of it.  A transaction with many transfers being used as input will cause the size of the transaction to go over the block size limit.  So for now try to consolidate your coins manually with smaller transactions. I've found the easiest way to do this is to use simplewallet from the binaries and copy/paste the command to send chunks of coins one at a time. When you send a group of coins that has a bunch of inputs into one destination address any future transfers of those coins will use that one transaction as an input.  In time, this problem will resolve itself. 

Hope that helps a bit.

-Jim