Version 10.2 was installed on my laptop (MackBook Pro) but it's not compatible with my desktop (IMac). 10.2 requires catalog "upgrade". Therefore, I no longer can use my external hard drive to be able to work on both machines since they cannot both use the same catalog. What's the fix?
I was able to open the catalog (from my iMac) that I was having trouble opening with my MacBook. It opened fine. Then, I tried to open the catalog again on my iMac and (magically) it opened just fine. So, for me, everything seems back to normal. Unfortunately, I am not able to shed any light onto the problem to help anyone else.