I was in the "Project Explorer" window, having previously expanded the drop down list for "Blank Project". With "Blank Project" still selected, I pressed the "?" button and got the following error message box:

http://img471.imageshack.us/img471/1676/editorerrormsg12qi.jpg

When I hit continue, processing resumed. But, the problem is fairly easily recreated. What caused this problem and what does the "?" button do anyway?

I take back my "easily recreated" statement. I was able to make it occur several times before I exited the Editor. But, going back in, I can't seem to make it happen again. A memory fluke?

Nice fluke! The '?' is a toggle to show only the files you added to the project or all files that match the wildcards you add in the includes. ..well thats what I think. Jorge will correct me if not.

How can I correct you Steve if, this is one of your many (nice) requests?

In fact, if you want to check for new files in folders included in projects, you can define which extensions to be searched using the [?].
To define the extensions add one line by extension under Tools>Options>Default Settings(more), like:
*.bas
*.bp

Remember that, in the above option you will be defining it for new projects, if you want to apply it to existing projects, you should use the Project>Settings>Includes.

As for the error, I believe it happened with you (Steven) for several times but, as it seems to happen there too, I can't reproduce it here, at least, one time.
Maybe, that happened during the first usage of the Editor and because something wasn't yet saved once.
I'll try it with a fresh installation.

Regards