How do I fix 'Setup project with custom action file not found' exception?

The answer is so maddeningly simple. If the last argument in the CustomActionData is going to contain spaces and thus you have to surround it with quotes and a trailing slash, you must also have a space following the trailing slash, like this:

/TimeToRun="[TIMETORUN]\" /TargetDir="[TARGETDIR]\ "

The solution and explanation can be found here.

Had a similar issue. In my case, it was odd because my installer had ran successfully once, then I uninstalled my app via Add/Remove Programs successfully, did some coding (did NOT touch my CustomActionData string), and rebuilt my project and setup project. It was when I re-ran my MSI that I got this error.

The coding I had done was to bring in more values of more parameters I had been specifying in my CustomActionData string. That syntax for getting the parameter values (i.e. string filepath = Context.Paramenters["filepath"]), which was in my Installer class, was actually fine, but as I found out, the syntax of the later parameters I was now trying to get from my CustomActionData string had not been correct, from the very beginning. I had failed to add a second quote around one of those parameters, so nothing else could be obtained.

I was using the "Textboxes (A)" and "Textboxes (B)" windows in the User Interface section. A has 1 box, EDITA1, where I get the path to a file, and B has 2 boxes, EDITB1 and EDITB2, for some database parameters. My CustomActionData string looked like this:

/filepath="[EDITA1]" /host="[EDITB1] /port="[EDITB2]" 

It should have been:

/filepath="[EDITA1]" /host="[EDITB1]" /port="[EDITB2]" 

(closing quote on [EDITB1])