"opener has no properties" when doing "add ph

I'm getting the above javascript error when finally clicking 'add files' in the add photos dialog. I'm using the option of taking the photos from a local directory. The images are found correctly.

I get this error when using mozilla 1.4. Everything works fine when using IE 5.0 under windows 98.

any idea?
thanks,
Hilbert
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Give us your Gallery/webserver information to get a faster answer.
Get this information from the PHP diagnostic (in the configuration wizard).
Gallery URL (optional but very useful): http://hilbert.xs4all.nl/gallery
Gallery version: 1.4-pl1
Apache version: Apache/1.3.26
PHP version (don't just say PHP 4, please): PHP v4.1.2
Graphics Toolkit: NetPBM
Operating system: Linux (none) 2.4.20-6um (debian stable)
Web browser/version (if applicable): mozilla 1.4