Micromaster LV48

[Squarewave]

.....once I'm in and select a device to read, I get the first error message. I occasionally see the second attached, when I retry to read an eprom.

[Squarewave]

Used the self test function on WinLV, passed all, results attached.

[giosif]

...
I found an old computer at work running W2000 Professional which has a parallel port.
...
When WinLv starts, I get the following messages, before I see the main screen.
Attachments: The two first error messages before the main screen is visible, then the third error message with the main screen behind, then the main screen loaded.

As far as I know, W2000 is not a supported OS for WinLV.
Also, don't quote me on this, but I seem to remember from back when I was troubleshooting my programmer that some people on another forum were discussing this kind of errors and it was due to them trying to use the WinLV software on WinXP (which also is not on the list of supported OSes and inherits the architecture of WinNT/W2000).
There might even have been a solution people found around this problem, but I might be confusing things with some other troubleshooting thread.
In any case, I'd stick to Win95 or Win98.

Used the self test function on WinLV, passed all, results attached.

This is great!
So, this means the CPU-related part of the programmer was actually ok all along.
What version of WinLV did you use this time?
Also, the self test checks the "analog" part of the programmer as well (i.e. the top board), so having all tests passed is really promising.
Looks like you are getting close to getting it working.

[coromonadalix]

would mean you're stuck on win 9x  era, nothing more ?      unless more recent Windows compatibility mode would work ??

NT  core is mostly win2k  Nt4 Nt 3.51 ... Xp 64 bit had some remnant, and was the 1st  public 64 bit os iteration  ,,, W7 W8 W8.1  ...

Win 8, not 8.1   was better to play with, it could accept non signed drivers, W8.1  become a pain in the ...

It depend on how the WinLv driver works and how the kernel permissions are made or be granted