Need non-negative Q-word to specify tool number with M61/Clears with G0?

Thanks, Andy.  I'll give that a try. I had dismissed this as being a potential source of the problem because it only fires off with the button press. I particularly like the guarantee of order of operations. 

I was wondering if it was firing randomly and briefly due to electrical noise. But that could only happen if it is a physical button rather than VCP GUI.

I know this is a older post, but I am experimenting a really similar issue.

In my case, I get this when I manually use use a M61 via MDI before loading a file. The file preview fail to be generated but the file load correctly. The error is generated when I load any file until I do a M6 tool change via MDI.

The g-code I load does not contain any M61. The message I get is:

Near line 1 of ...
Need non-negative Q-word to specify tool number with M61

Do you have any tool change remap or similar active? Can you tell us more about your system?
What are the actual first few lines of the G-code?