What are you trying to execute? How are you trying to execute it?
I don't know how big your program is, but assuming it is a single c source file and you are not using make - then you may be doing something like this.
> cc myspell.c
> chmod 755 a.out
> ./a.out
Anyway, the error that you have recieved is telling you that the file that you have compiled is not a valid executable file under your current operating environment (OS and or hardware combo). It occurs when a request is made to execute a file that, although it has the appropriate permissions, does not start with a valid format.
Did you compile the program and try to run it on a another machine?
Or perhaps your uni is using NFS to mount the server partitions. NFS is a little slow in keeping files updated - the error is common when compiling on machine and executing on another, so once you have compiled your executable try using the sync command to ensure the files are updated.
> sync
