Thanks for the suggestions.
Renaming vrestore.slk or vslick.sta didn't help. Neither did making minor changes to the menu.
However, what did work was the following:
- Delete the Send Output to Editor Window item from the menu
- Close the .process buffer editor tab
- Issue the toggle-process-tab-output command at the command line -- Process already running message resulted in the status bar
- Issue the toggle-process-tab-output command at the command line again -- no message in status bar
- Put the Send Output to Editor Window menu item back in.
Note that I don't know if steps 1 and 5 were actually needed. Also, I haven't tried to turn this on and off with the menu again, but at least I can build again without getting the .process editor tab.
Perhaps the 'Process already running' message in step 3 is a clue to why it didn't work in the menu? I don't remember seeing any message, though, when I tried to turn it off with the menu.