Quote from alanm:
I would first guess that it has something to do with not having sufficient funds to take a position in the underlying.
Could also be a communication issue, based on the OP's apparent inability to accurately describe the exact scenario here.
Quote from rabmanducky:
no sorry I just reread what I wrote.
I mean why do some brokers don't allow clients to buy a stock and then excercise a put. Or conversly sell a stock and then excercise a call. Alot of brokers force you to excercise first and then do the buying and selling of the underlying. But allowing clients to buy and sell the stock first, and then excercising would seem to limit the risk to the client.