In the mean time I submitted this Signability behaviour as WDK feedback.
In the answer some kind soul told me that the “ Inf2cat tool replaces
the Signability tool”.
Inf2cat is part of the Winqual submission tool, the download is free,
and it works. A link to the FAQ is here:
https://winqual.microsoft.com/Help/default.htm#Inf2cat_FAQ.htm
Thanks to the Microsoft Windows Driver Kit Documentation Team! 
Hagen Patzke schrieb:
On an XP SP2 system with German language settings, the WDK tool
Signability.exe (from WDK RTM) reports the error“Signability Test failed to run, TestDrivers function call failed.”
when in the driver INF file DriverVer is set to December, 2006.
Examples:
DriverVer=11/30/2006,6.0.6000.16386 ; Fine
DriverVer=12/01/2006,6.0.6000.16386 ; Provokes error
DriverVer=01/24/2007,6.0.6000.16386 ; FineDecember 2006 is over, so currently I am not affected by this problem.
Nevertheless I wonder whether - according to Microsoft - German years
might have only 11 months, as opposed to English ones…> Udo Eberhardt schrieb:
>> Based on your surname, I suppose you are located in Germany…
>>
>> The Signability tool seems not to work correctly if the system is set
>> to German data/time format. In Control Panel - Regional and Language
>> Options set “Standards and formats” to “English (United States)” and
>> try again. After you are done with Signability you can switch back to
>> German.
>>
>> UdoI did not try it, but it could also work to use the Microsoft AppLocale
Utility and run Signability.exe with an English locale.Can someone tell me how to report this bug to Microsoft?
IMHO for fellow developers a KB entry might be helpful.
-H
