If it fails, make sure it fails right.

A short, recent story:

A customer complained that he gets 403 Forbidden trying to access the userTrack dashboard. Everything else was working (tracking, API, etc.).

After several days of via-email troubleshooting I got access to the server to check the error myself.

The index.html wasn't uploaded...

Conclusion: Your product/service can always break in some way. It's more important to show relevant error messages instead of trying to avoid all the ways in which it can break. A solution in this case would be to have a list of "required files" and after installation alert the user if any file is missing.

PS: I have no idea how that file was missing, userTrack is uploaded as ZIP archive containing all the files.