Dear Jerry,

You helped me a great deal. Now tex-file works alright except for one
minor glitch. After I try to execute the same tex-file command for the
second time I get an error message: processp, nil

If try tex-file again, it works again. So every other time it works and
every other time it fails.

I am not sure if it is of relevance but, just in case, I attach here the
process-environment value:

I don't see anything suspicious in your environment. Please try the following. Set the variable debug-on-error to t (this can be done via the menu, although I've forgotten where that menu item is on 21.4). Then make the processp, nil error occur. If you get a debug buffer with a stack trace, please email that stack trace to us. If you don't, then set debug-on-signal to t (which can also be done via the menu) and try again. Thanks!