[Solved] I can't switch between themes anymore

[Hercules24]

After a few months I wanted to change to a different theme in CPG, but when I select a different one in the config menu and press 'save' CPG says 'Coppermine configuration was updated', but when I check on a different PC I still see the old theme showing, and when I check back into the config menu the old theme is still selected.
The only way to get to the desired theme is to delete all other themes, or to rename your desired theme to the one that seems to be 'locked in' to CPG.
I'm sure this is something simple and stupid that ocured while updating or modifying my theme, but I can't find out what caused this.
Link to my gallery: http://www.kuikens.com/pictures/index.php
Current theme is Kuikens1 (with a small line of 3 advertisers), but I'm planning to show theme Kuikens without ads.
I hope someone can help me out here.

[Joachim Müller]

Site displays as expected for me (using the theme Kuikens for me out of the box). Reset your cookies.

[Hercules24]

Thanks Joachim, it seemed to be a cookie issue.
Problem solved.