Run time error 59201

Run time error 59201 appears when my UserForm1-mask is called, it appears before mask is formed and then the program's execution is interrupted.
Together with UserForm1's forming, my VB macro (VBA 5.0 in Excel07) is supposed to create a new Excel folder to save values tipped in mask.

UserForm1 is called via a new menu point that is created with source-code from the same macro, this doesn't seem to be a problem for Excel! It works!

I don't know what's the matter with my mask and why this error 59201 appears.

Thanks for any help.