WP Admin not accessible to administrators after plugin activation

Hello – I installed a plugin “Advanced Access Manager” and got an error display on accessing that plugin in WP Admin. The error warning isn’t important (I think) but stated “Warning: array_merge()…Argument is not an array in …./advanced_access….model/api.php”.

I decided to deactivate the plugin but had to first step away. When I came back to my laptop I had to log back in. When I did, none of the usual functionality was available in WP admin, but I was able to login. The other administrator login gets no admin access at all.

The front end content, however looks ok.

Can I restore a default permissions structure for access to admin. I do have access to another install of WP.

Thanks for any help you can give

A