VsixSignTool.exe Error Code 0x800700d - The data is invalid

I'm getting an error with the VSIX Sign Tool. I'm using build 14.1.24720. My command line is: 

Start-Process $ToolPath -ArgumentList "sign /f cert.pfx /sha1 ‎‎<sha1> /p $Env:signing_code /v /t http://timestamp.digicert.com $VSIXPath" -NoNewWindow 

This is run as a post-build step in Visual Studio. The weird thing is it used to work with the same command line. What differs is the certificate. My issue is that I've now generated several certificates and re-keyed the one that was working and none of this works. I'm at a loss as to what data is actually invalid.

Any help would be greatly appreciated!