Attaching a couple test computers to an isolated router with a printer might help point to the problem.
The problem is caused by running a 32 bit program on a 64 bit windows OS and the 32 bit program sending a request to the printer that the print driver cannot handle. The error is commonly known as thunking spooler error or thunking spooler stops working
Have solved the problem in 2 ways
Firstly form within my filemaker database set up a script to select the printer the user wants to print to and then printed each report the user wanted to print using filemaker scripts. The user was not able to access the printer dialogue box during printing and hence no request was sent through a dialogue box to the printer during the act of printing.
Secondly and this is the best solution. Find the latest drivers for the printers, that are less than 3 years old, replace all network and local drivers, (a multi model print driver is best if it is available). This replacement is not completed yet on our network but I cannot get the error "printer not connected to the port" on any local machine that has had the drivers replaced.
I am in the process of writing a script to do a startup replacement of the drivers on all local computers and an out of hours print server driver update by doing a spooler stop , an explorer end process tree, an explorer application restart, followed by a replacement of the drivers in the C:\Windows\System32\spool\drivers\x64\3 directory, then spooler start. The latter method which is going to be done on the server has been tried on various local computers and it works a treat.
How all this was found out
A printing specialist from FujiXerox came to see me and he said the problem has been known about for 3 years or more. The way I undersand it is as follows. The problem occurs whenever a 32 program on a 64 bit computer sends a request to a printer that is running a driver that cannot handle the request properly, the request remains open and the program cannot print, this is called thunking.
This can happen within filemaker, 32 bit office doing a mail merge or many other 32 bit programs running on 64 bit windows.
The problem has been around since 2009.
From what I have been told most of the later drivers do not have this problem. So get the latest multi model print driver and install it.
Thank you for the very complete documentation of this issue and the solution! Many folks that find their solution independently of this forum forget to come back and post what solved the issue and then we don't have that info available to help others.
Whoda Thunk? Makes sense. Stepping back far enough to see the forest has always been a challenge for me.
Thank you for the insights, when I run into a tech who knows his stuff, I often ask where else I could find this out. Often the only answer is "Ask me."
This Google examines thunking