Logout after clicking any "Banner Slider" link in the top navigation

[Subjekt2Change]

I am currently trying to add a few banners to existing sliders, however every time i click on a sub-navigation link ("Manage Sliders", "Manage Banners", "Preview Slider Styles" or "Report Banners") i get logged out. After logging back in the error message "Invalid Form Key. Please refresh the page." is shown.

All the other navigation links are working fine.

Searching for the error message has revealed that a few users have had the same issue, however only in the admin login form. Regardless i tried the mentioned solutions to no avail:

• I refreshed the cache.
• I deleted both the var/session and the var/cache folders.
• I made sure the cookie_domain and cookie_path database entries are correct.