We have over a dozen SQL servers, one of which hosts a couple of hundred sage databases, when i right-click on the Databases node in SSMS there is a long delay then i get the following error (and the restore dialogue box doesn’t load):

I presume SSMS is loading backup history from msdb or something in the background and running out of space - does this imply i have excessive backup history in my system databases? If so, what is the best way to maintain it?
I have maintenance plans cleaning up the trn and .bak files on disk but i dont think i maintain any of the logs in the system databases.