Have you tried restarting?
Many times. I first saw this error with LR 5 and now with LR CC
That error appears in many dialogs. I'd call it the most useless error message ever. Apparently it's never meant to get out to the user.
I wonder if it isn't catalog specific. As an experiment, you could try going to All Photographs in the Catalog panel of Library, then going to File>Export as Catalog. Leave 'Export Negative Files' and 'Build/Include Smart Preivews' off and 'Include available Previews' on.
How long this takes depends on the size of your catalog. Open the newly created catalog in Lightroom and see if you can delete the collection then.
If you're successful you could continue with the catalog. There's one caveat: Publish Collections don't export to the new Catalog.