HTTP 500 Internal Server Error after theme activation

Hi,

When activating my theme throughout my WP site, I got an HTTP 500 Internal Server Error and can’t access my dashboard (either network and site, as I’m working with a multisite configuration).

Thus I renamed my theme in the FTP and I can access my dashboards again. But when re-installing it, I got the same error message.

How come can I solve this, without reinstalling all my website? It looks like my site has registered this theme somewhere..

Please help me

Cheers