Error loading include file 'T4Toolbox.tt'

[LandOfToz]

Invoking Text Transformation in a VS Extension (https://msdn.microsoft.com/en-us/library/gg586947%28v=vs.120%29.aspx?f=255&MSPPError=-2147217396) results in the following error:

There was an error loading the include file 'T4Toolbox.tt'. The transformation will not be run. The following Exception was thrown: System.UriFormatException: Invalid URI: The format of the URI could not be determined. at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind) at System.Uri..ctor(String uriString) at Microsoft.VisualStudio.TextTemplating.VSHost.TextTemplatingService.CheckSecurityZone(String path) at Microsoft.VisualStudio.TextTemplating.VSHost.TextTemplatingService.LoadIncludeText(String requestFileName, String& content, String& location) at Microsoft.VisualStudio.TextTemplating.Engine.ProcessIncludeDirective(Directive directive, ITextTemplatingEngineHost host, VisitedFiles includedFiles)