Forms executable files are platform specific. So you can open your fmb file on your Windows Developer suite client and compile to just check errors on your code.
However to make it work on your UNIX forms server. You need to,
1. ftp the fmb file in binary mode to your unix server
2. Use f60gen to generate fmx on your unix box
Sorry in my previous reply I had type ascii instead of binary
Did you change to binary when ftp?
By default, is ASCII.