XLToolbox 7.3.4 fails to install on Excel 365 with a Certificate Not Trusted error


#1

I’m able to double-click on the XLToolbox EXE file to install it.
But in Excel, when I try to add the XL Toolbox COM add-in, I get the following error message dialog box:

“Customized functionality in this application will not work because the certificate used to sign the deployment manifest or its location is not trusted.”

I’ve attached a screenshot of the software failure.


#2

The only way to solve this would be for me to purchase a code signing certificate, which costs lots of $$$/€€€ and has to be renewed every year. That’s not sustainable with the current business model. I am extremely unwilling to make the XL Toolbox commercial software and stop giving it away for free, but it may very well be that this is the only way to prevent errors such as this one.


#3

I believe there are ways to get FREE code signing certificates.

Would this work? Or is this something that I have to do, since I’m the administrator on the computer I’m using at this moment.

https://blogs.msdn.microsoft.com/emeamsgdev/2014/06/10/how-to-create-and-use-a-code-signing-certificate-for-clickonce-vsto-applications-using-active-directory-certificate-services/


#4

I found a solution!

This little application will modify the Registry to override that security setting and give me the option to install XLToolbox.

XLToolbox is working fine now.