I asked and answered by myself...^^;;
i found my fault...That's because of the difference VARTYPE() with TYPE()
function. i usually used VARTYPE() but in case of _screeen parms, VARTYPE()
causes error, Hacker's Guide said that.
Huh~ i spent a whole day to debug this with only used VARTYPE() even in the
debugger. i put my head on the table and murmured to myself..idiot.

Thanks.
HK.Lee