[Plugin: NextGEN Gallery] Problem with image upload

Dear Mr. Rabe,

I’ve been using your plugin for some time to organize and display images on my homepage. Since now, I have been very content with its usability and variety.
A short time ago I transferred my wordpress installation to another folder on my server. Everything seemed to be working fine in the first place. But when I tried to upload a new gallery using the zip-archive upload of the NextGEN-plugin, I just got the message:

“0 picture(s) successfully added”

When I tried another zip, four pictures were added but it was impossible to add the rest.
I checked the gallery folder on my server with my ftp-programm. All images have been uploaded, but they do not appear in the backend of wordpress and there are no thumbnails created.
I read some old forum posts and somebody mentioned that the problem could have something to do with the .htaccess-files. Perhaps you know more about this problem.

I use wordpress 2.9.1 and NextGEN Gallery Version 1.5.5.
These are the server-stats displayed on the dashboard of NextGEN gallery:

* Betriebssystem : SunOS (32 Bit)
* Server : Apache/2.2.17 (Unix)
* Speicherverbrauch : 19.16 MByte
* MySQL Version : 5.0.91-log
* SQL Modus : Nicht gesetzt
* PHP Version : 5.2.14
* PHP Safe Mode : Aus
* PHP Allow URL fopen : An
* PHP Memory Limit : 104M
* PHP Max Upload Gr??e : 10M
* PHP Max Post Gr??e : 8M
* PCRE Backtracking Limit : 100000
* PHP Max Script Execute Time : 30s
* PHP Exif Modul : Nein
* PHP IPTC Modul : Ja
* PHP XML Modul : Ja

* GD Version : bundled (2.0.34 compatible)
* FreeType Support : Ja
* FreeType Linkage : with freetype
* T1Lib Support : Nein
* GIF Read Support : Ja
* GIF Create Support : Ja
* JPG Support : Ja
* PNG Support : Ja
* WBMP Support : Ja
* XPM Support : Nein
* XBM Support : Ja
* JIS-mapped Japanese Font Support : Nein

Thanks for your help.

Regards

lomdt