[Haskell-beginners] hClose: illegal operation (handle is finalized) and/or <<loop>>

[Travis Erdman]

I read in some data from a file (via decodeFile), process it, and write the 
result back to a file.  My last line of code is ....

encodeFile (filename++".sol") (gametype,gstree,newiterlist,newstamplist,result)

and it is all of the sudden now causing this run-time error:

mincfr: kclv5.sol: hClose: illegal operation (handle is finalized)

It has been working fine for quite a while, but now quite mysteriously gives 
this error.  (But obviously I have been heavily tinkering with the processing 
part of the program).

If I remove the encodeFile line and instead ...

putStrLn $ show result

I get this run-time error:

<<loop>>


Help?

thanks,

Travis