OOPs!!! Whats this now? Why am i getting this error when I try to go to my dashboard.

I am getting this error when I try to go to my dashboard:

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 77824 bytes) in /home/content/06/8426106/html/wp-admin/custom-header.php on line 732

All I did before this was - tried to activate my bbpress plugin and I received the same error....and there after I am getting this error even if I try to go to my dashboard - superadmin/admin what ever?

Kindly help, and its urgent - I can't do anything...

thanks in advance