this morning I tried the code on a Windows2000, it works perfect.

yes, the reduced code fail the very same way as the full-sized program. the only minor difference is that in the error message it will be "image2" instead of "image1".

it is interesting that if I click the "New Window" button and then click "Select File" button in the 2nd window first, it works(!) for the 2nd window, but will fail for the original window this time. No matter if you destroy the successful window or not.

this phenomenon seems to suggest that the FBox object definition has difficulty in multi-entry.

I tried to read the source of FBox.pm. however, I cannot see a easy fix. Or should I contact the Perl/Tk mantainers?

Probably Perl/Tk developers are active on perlmonks.org. Then I shall not need to pray in another temple:-)