>>>>>I can't compile the help system (with HTML Help Workshop), until I either close VFP, or SET HELP OFF. I get an error message, stating that the help compiler can't open the CHM file.
>>>>>
>>>>>This is strange, for when my SET HELP doesn't involve the help file I want to compile:
>>>>>
>>>>>

>>>>>set("help") = "OFF"
>>>>>set("help", 1) = (the standard VFP help file, ...foxhelp.chm)
>>>>>

>>>>>
>>>>>Since this only happens after I had opened the compiled CHM file in VFP, it seems obvious that the file is somehow in use, despite the fact that on shutdown, the main program sets help back to the standard VFP help.
>>>>>
>>>>>Any ideas?
>>>>
>>>>When does ON SHUTDOWN fire?
>>>
>>>The problem I mention is after quitting my application, and returning to the VFP command window. The problem only appears if at some moment I did open the compiled help file.
>>>
>>>So, there is no active ON SHUTDOWN.
>>>
>>>I can circumvent the problem by issuing SET HELP OFF, but I still find this weird.
>>
>>If you are running your application in the development environment and then quiting to the command window, ON SHUTDOWN is not firing to release the help file. ON SHUTDOWN does not fire until you EXIT foxpro. Try putting a messagebox or something in the ON SHUTDOWN routine so you can see when it fires.
>
>I don't see the relation.
>
>My application does have an ON SHUTDOWN, which fires when I press Alt-F4 (or give the File | Quit command).
>
>The cleanup procedure sets the the help file back to standard VFP help, and I verified this with set("help", 1).

It's possible that I am off track here, but it sounds like you are running your app in the development environment either from the project manager's run button or directly from the command window, and then returning to the command window when the app quits. If this is true, your ON SHUTDOWN routine is probably not firing since it fires when you quit VFP NOT when you exit your app. You can test this by replacing your ON SHUTDOWN command with

ON SHUTDOWN messagebox("Shutdown in progress.")

Then run your app , quit your app and see if it fires.
If you are absolutely sure it is firing, set help off followed by set help on in your routine might flush it for you.
I'm certainly not an expert here but I have noticed some unexpected behaviour with ON SHUTDOWN. If you are running in the development environment, what commands are being executed when you issue FILE|Quit? Certainly not a QUIT or you would be leaving VFP. More likely its a CANCEL. Also, it's possible that when you set the help back to standard foxhelp, you are only resetting a pointer and it doesn't effectuate until you reissue the HELP command.
Some things to think about anyway.