Gary B: GauGau is right. Let me sum up what I would suggest for your problem, and then it's up to you. If you discover more troubleshoting info, please post in the plugin thread (with a quick summary and link to this thread if it's related).
That query is so simple as I said. There's a COUNT() function and a table and that's it. If you copy that query to phpMyAdmin and it executes fine, then I don't know why Coppermine cannot execute it. I assume your bridge with phpBB is working correctly otherwise. Do you have any other plugins or mods installed? Are there any issues with your bridge? I assume Coppermine uses a similar query in the user manager or groups manager. You could try gonig to those pages and checking the debug info looking for queries that reference the same table as the one having issues here. I don't know enough about bridges but could it be this table you mentioned is in a different database with different connection info and this plugin doesn't initiate this connection before running this query? All the previous queries to this problematic one are with Coppermine core tables so that's one difference with this query: it uses an explicit database name and a non-Coppermine table.
The original mod thread that Nibbler posted (linked in the first post of this thread) mentions you have to change things for your bridge, but I doubt that that's necessary in the current plugin version but I really don't know.
So those are my suggestions for things to consider. Please try out what you can - troubleshoot the problem. Then, when you have more information, summarize what you did & what you found and post in the plugin thread.
Over and out.