I have been going nuts with the fatal errors. I found this remark in Alex Rabe’s FAQ for NextGen Gallery—
When I try to activate the plugin I get the message : “Plugin could not be activated because it triggered a fatal error.”
This problem could happened if you have a low memory_limit in your php environment and a lot of plugins installed. For a simple test deactivate all other plugins and try then to activate NextGEN Gallery again. Please check also if you have a minimum memory_limit of 16Mbyte (as much as possible).
After increasing my php memory from 8mb to 16mb, the issues went away.