24 Jun 14, 07:15AM
Although it doesn't look like this is the problem, AC dmo files are gzipped, and some upload sites give you an unzipped file. If you open it with a text editor, does it start with "ASSAULTCUBE_DEMO"? If so, it's been unzipped and you'll need to gzip it.
It could also be that the file is corrupt. If you don't mind anyone seeing it, you could always share the link and see if anyone can identify the problem.
It could also be that the file is corrupt. If you don't mind anyone seeing it, you could always share the link and see if anyone can identify the problem.