There are a number of likely reasons why TEX can't find a file:
- The file does not exist in either the current folder or in any of the
subfolders within TeX-inputs.
If TEX was looking for a format file then make sure it is in the
TeX-formats folder.
- You could have spelt the file name incorrectly.
- The file name might contain an illegal character.
A Macintosh file name can contain just about any character, but
TEX is not so flexible.
Don't use spaces and avoid non-alphabetic characters in all file names
that might be seen by TEX.
If you see such an error then the best thing to do is hit Command-dot
to abort TEX and either rename the file or move it to the correct folder.