Glass Mapper t4 null or empty string

Question

I'm trying to setup Glass Mapper to generate my Sitecore items. I've followed every tutorial I could find, but receive this error when attempting to generate the code:

"Loading the include file 'Helpers.tt' returned a null or empty string. The transformation will not be run."

A file is generated but repeats the word "ErrorGeneratingOutput" over and over.

Screenshots:

Answer 1

Have you tried to click the unblock button in the properties window of the file?

Answer 2

As well as what Ehab has suggested, you may also have to remove the empty line at the end of GlassV3Header.tt otherwise you will get a error:

An error occured while generating code for item '/sitecore/templates'.
T4 Template: D:\Project\XYZ\TDS.Master\Code Generation Templates\GlassV3Item.tt

Errors:
Compiling transformation: Invalid token 'this' in class, struct, or interface member declaration     
Compiling transformation: Method must have a return type     
Compiling transformation: Type expected

Crytic, but deleting the extra line solves the issue.