Install NI488 for PCMCIA-GPIB fails - unable deleting NI-VISA 2.6.0 Runtime

I tried installing NI488.2 312 on Win7 pro 64bit.
unfortunately there came a message "Unsupported version of NI-VISA detected".

there had been installed visa260runtime.exe which I need for a logger program.

anyway I tried uninstalling this NI-VISA 2.6.0 Runtime using windows 7 "Programme und Funktionen" "Ändern". Unfortunately this failed. If I try again I am getting a message: "Warten Sie bis die Deinstallation bzw. Änderung des aktuellen Programms abgeschlossen ist". But nothing seems to be running.

How to get rid of this NI-VISA 2.6.0 Runtime so that I can successfully restart installing this older NI488.2 version supporting this PCMCIA-GPIB card?

on a Win 7 pro 32bit I got this to work. Now I try Win 7 pro 64bit.

could you please give me a hint how to proceed?

Best,
Matthias