Code signing doesn't work - can't find file

[reflex]

I'm using Visual Build Pro 9.6 (x64).

I can't build any projects that have code signing anymore. The error message is:

27/06/2018 11:40:32: Building project step 13 - Sign binaries...
Processing file 3 of 4: w:\dev\flstudio\Plugins\Fruity\Effects\Fruity Convolver\FruityPlug.dll
27/06/2018 11:40:32: Building project step 14 - Sign (SHA256)...
Verifying signature...
Failed to create process: The system cannot find the file specified.
27/06/2018 11:40:32: Step '14 - Sign (SHA256)' failed
27/06/2018 11:40:32: Build ended (elapsed = 00:00:32).

The file that has to be signed is present in the indicated location (it's built by the project).

As far as I can tell, this started after installing Visual Studio 2017 Community Edition, so I have the impression that Visual Build Pro has a problem locating signtool.

I have looked for signtool.exe and it appears in various locations. See the image at this url for a list:
https://www.dropbox.com/s/zv2hgxxnrl...ntool.PNG?dl=0

What can I do to make sure Visual Build Pro finds signtool? Is there any way to get more information about this error?