THANK YOU nhnorsker!!!
I just spent a couple of figuring out how to get my Library to open, got in touch with the tech support, it did not work. All the other options were tried to no avail. This one solution works, many thanks to Thorgrim and you. And copying the pdf file content works, but I tried to also copy the rdb content (maybe my groups are there??) but it messed up things again, so I reverse that, and I just have to regroup my refs… again, I am just happy to be able to open it again and to have the pdf.