Adobe forms - USAGE_ERROR

Hey, Adobe form Gurus,

I created an Adobe form and I can printed it correctly from an ABAP program.

But when I copied the codes from ABAP program and made a remote function module, I got USAGE_ERROR after the CALL FUNCTION I_FUNCNAME.

Again, if I copied the codes from function module back to another ABAP program, it worked.

Is something I missed?

Thank s in advance!

Fisher Li