Plugins crash admin area

[gpannequin]

Hello,

I have the Enterprise child theme with the following plugins:
- CMS Tree Page View
- Google Maps for WordPress
- Simple Fields

I tried installing the plugins "Contact form 7" and "Custom field template" (replaced the last one with "simple fields") and when I activate either of those I have an error 500 on every page of the admin area. The front, however, is fine.
I have to delete the plugin directory to get my admin back.

Is this a theme/plugin incompatibility? Couldn't find anyone else having this problem.

I don't know if this is important but my FTP connexion is secured, meaning wordpress can't install plugins via the admin, I have to manually upload them via FTP.

Thanks