Go into your query in design mode.  Change the PaymentType to PaymentTypeID (Access is still looking for the field you renamed.  Renaming as you have found out doesn't always propagate through out forms and queries of code.  One of the down falls.

As far as question 1 - you might be able to hit the Pause / Break key. but in this case I don't think that would work.
Unfortunately that gives you 2 alternatives.  1) click 300 times.  (be glad it wasn't 10k) or 2) go down to the task bar.  Right click and go to Task Manager.  Find Access - Right Click and click End Task.

NOT a great way to shut down your data base.  You have the potential of corrupting it but sometimes you don't have a choice.
This brings up another important reason to Work with a Copy first when making major changes AND Backup, Backup, Backup!

Here's the goofy thing - the data type updated to PaymentTypeID in the MemberPayment table I could see in the query. I couldn't see any instances of any of the other tables having the old PaymentType. I deleted all the mentions of the PaymentType in the query itself, and STILL had the problem. Today I will try rebuilding the query from scratch to see if I missed something - and use a stripped-down data table so I don't have to go through all that crazy OKing of error messages. Yes, thank goodness it wasn't 10,000!)

I have backups, so it's no problem. (And a benefit of having a split database - you can just replace the backend!)

Aha! I was unsmart and didn't go fully downstream to start making the changes. When I've got queries based on queries, I need to be careful. I have a list of all my queries, but I think I also need to draw maps!