It's very likely because your wallet is littered with a TON of small stake transactions/blocks.

Make a new address, then send yourself a payment. If it fails, send a smaller one. Keep trying til you get it to work.

Then send 2-4 more.

Then try increasing the amount.
It happens because you're trying to send, but there are too many inputs. It's like buying a xbox game at Walmart with pennies. The cashier may look at you and say "no"

You need to consolidate them into larger blocks. You do this by sending the biggest payment you can to a new address you own. Then consolidate those.

It's a PITA block chain limitation. Our JPC wallet was dead and unable to process a withdrawal for about 6 hours one day while I figured out wtf the problem was. Had to send ourselves increasingly larger payments to consolidate all the small deposits from people mining to their AllCrypt wallets.

Give it a shot.