WordPress MU

I have been experimenting with registration plugins. Everything has been working fine but suddenly, only on my main blog, after logging in or when logged in and selecting to view my dashboard, I get an error 500. I can manually enter the url for any of the admin menu items (except the dashboard) and it work fine. The dashboard also works fine on my user blogs. I am using the latest version of wordpressMU (2.6). Can anyone help?

"experimenting with registration plugins"

Umm, go back to a state where it all worked and try something else.

Disable all plugins, test, disable half, test, disable half again . . .

WPMU is not the same as WP for registration. IN WPMU there is no registration.

I have disabled and re-enabled each plugin manually and still have this problem. It seems that when I initially login to my main wordpressMU blog and select to visit the site admin page ("blog"/wp-admin/), I get the error 500 page. I then manually type the url of an admin screen such as (../wp-admin/themes.php) and it takes me to the correct page. Within the admin, if I then select the tab for my main blog, which would take me to my dashboard via, (../wp-admin/), I don't get the error. If I go back to viewing my blog and again try to return to (../wp-admin/) I get the error again and have to type the url of an admin page to get in. Again, this only happens on the main blog. The sub-blogs all work perfectly fine. Any suggestions?

check your error logs.