I guess my provider uses php safe mode, so php cannot write into cache directory when generating thumbnails.

I get these errors:
Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06439.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06440.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Any ideas how to solve it???

Thanks a lot :-)

I don't think that missing library is the problem. I do have v2.0.4 and this is the complete output in debug mode. So I really think that PHP safe mode is the problem.
I also cannot change directory permissions since I have only ftp access.

See the output.

Simple Image Gallery PRO Notice: Joomla!'s "/cache" folder is not writable. Please correct this folder's permissions.

Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06439.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06440.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06441.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Warning: imagejpeg() [function.imagejpeg]: Unable to open '/DISK6/WWW/jirkatesar.eu/joomla/cache/jwsigpro_cache_c98bc4f10fdsc06442.jpg' for writing: Permission denied in /DISK6/WWW/jirkatesar.eu/joomla/plugins/content/jw_sigpro/sigpro.engine.php on line 293

Hi there!
You said that the cache folder of your joomla isn't writable, right?
That means that the caching system of the joomla isn't working, right again?
Is it possible to turn off the safe mode? I don't know if your provider permits that.

Thank you!

Yes, exactly as you wrote. My provider unfortunately does not allow to switch safe mode on. Is it posible to have the Gallery without caching?