I have the exact same problem.  I have entered various dollar amounts from $50 to $5,000 and tried to process the returns.  Each time (about 12 times) I get the same error about nt enough refund money available to buy the "I bonds."  What is wrong with the program?!  Get the thing fixed...NOW...not at some vague deadline over the next two years!  Yep, I'm angry...wasted so much time trying to troubleshoot the program.