As I've been implementing all the helpful advice members have been providing, I suddenly received an error message when attempting to filter:
And it's not just this schedule; filtering no longer works in any of my schedules. In fact, the filter button has even been removed from the menu bar.
I had this happen once before, and the only solution I had was to redirect to a previously saved database (I am using a SQLlite database). Fortunately I recently saved my entire database, and I export the XER schedule often. (Although, I should be doing an XML export)
So I'm not devestated, just set back an hour or so.
Has this happened to anyone else?