Critical error code - but why?!

I just installed SIGE and wanted to customize it as shown on the demo page. But whenever I add a parameter like crop=1 I get an error code that I dont understand.

[sigplus] Critical error: Image gallery folder tegning/blyant,crop=1 is expected to be a path relative to the image base folder specified in the back-end.

Whenever I don't use the customization codes It works with no errors.
I'm confused and annoyed. The plugin is the perfect solution to my website if I can only get it to work!