(SOLVED) Unable to remove printer driver from Windows 7

I was contacted by a customer few days ago with yet another challanging problem. He called and said: “Luka hi, we can't upgrade or remove some printer drivers from one third of our Windows 7 x64 SP1 machines.”

The error message when we tried to remove different printer driver packages was:
Failed to remove driver HP Universal Printing PCL 6 (v5.2). The specified printer driver is currently in use.
Failed to remove driver HP Universal Printing PCL 6. The specified printer driver is currently in use.
Failed to remove package hpcu111u.inf. Driver package is in use.

and

Failed to remove driver Kyocera Classic Universaldriver. The specified printer driver is currently in use.
Failed to remove package oemsetup.inf. Driver package is in use.


I started troubleshooting this and tried almost all suggested solutions I could found on the net like:
- stop / start spooler
- reboot to safemode and unistall driver from there
- msconfig disabling all non Microsoft services
- cleanspl.exe
- logged on as every user, deleted both the printer and the driver
- disabling bidirectional support
- RUNDLL32 PRINTUI.DLL,PrintUIEntry /dd /c \\MachineName /m "AGFA-AccuSet v52.3" /h "Intel"
- printui /s /t2
- MS forum post: Deleting Printer drivers from Vista system 
- MS Answers question: Trying to un-ininstall print driver error message ...
- Skidzopedia post: How To Fix “Cannot remove or delete network printer” Error in Windows 
- and probably other solutions that also didn't help ...

At the end I found interesting workaround that went like this:
1. First I removed printer in "Devices and Printers"
2. Then I stopped print spooler
3. In registry I opened

HKLM\SYSTEM\CurrentControlSet\Control\Print\Environments\Windows x64\Print Processors\

4. I renamed all Print Processors that were listed. Like Winprint to Winprint.old, Hpcpp107 to Hpcpp107.old, and so on ...
5. I started print spooler
6. Removed problematic driver pack in Print Management MMC
7. Reopened registry location

HKLM\SYSTEM\CurrentControlSet\Control\Print\Environments\Windows x64\Print Processors\

8. Renamed back all Print Processors to original name. Like Winprint.old to Winprint, Hpcpp107.old to Hpcpp107, and so on ...
9. Restart print spooler
10. Installed new printer drivers
11. Tested printing

Maybe this procedure will also help someone else with similar problems :)

This is it for today. Have fun!