Software fails to start since feature update to Windows 10, version 1803 - returns .NET Framework Initialization Error "Please set registry key HKLM\Software\Microsoft\.NETFramework\InstallRoot to point to the .NET Framework install location"

Hi, 

My software fails to start on any PC that has put through the Feature update to Windows 10, version 1803, returning this error:  

".NET Framework Initialization Error
Please set registry key HKLM\Software\Microsoft\.NETFramework\InstallRoot to point to the .NET Framework install location"

We packaged it with Spoon a while ago and that could be the cause, but we can't repackage it and are looking for a workaround. Any suggestions/methods that I can employ to get the software working in latest Windows 10 update without repackaging? Thanks!