The ".inc" statement points to a .sub file in the sub directory not a .txt file. Is your .sub file saved as .sub or .txt? All .sub files, the spice models, must be saved as .sub and nothing else, otherwise it throws-up leaving one scratching their head.
MrCecil, this is totally bogus. The file pointed to by the .INCLUDE directive can have any extension you like, including none at all. The file must contain text, and must contain a valid Spice subcircuit bounded by .SUBCKT xxxx pins and .ENDS. xxxx must match the third, or fourth attribute on the symbol placed in the schematic...
If you don't believe it, unpack the zip file I just sent to RonV.