[Plugin: Booking Calendar] installation errors

Here’s your first stop:
https://www.wprecipes.com/how-to-increase-wordpress-memory-limit-the-easy-way

Gee, it looks like you have a pretty high setting already, about 30M.

If that doesn’t do it, I’d talk to your host about raising the php memory limit.

You might also ask the author of Booking Calendar, he’s a very helpful guy.