Showing the complete path to the script would show the version of the compiler used, which might be a key clue.
On Linux, when providing the script a bad value, the error received typically looks like this:
$ source /opt/intel/Compiler/11.0/083/bin/ifortvars.csh ia3
ERROR: Unknown switch 'ia3'. Accepted values: ia32, intel64, ia64
Maybe it can be determined what the script sees in your case for the argument if executed this way (adjust the path accordingly for your compiler version installed):
csh -x /opt/intel/Compiler/11.0/083/bin/ifortvars.csh ia32
