First, double check that this is still problematic. If so, test if the file can be uncompressed locally on your own computer. It may have compression problems or be incomplete in some way. On rare occasions, a local uncompression will function but a direct upload will not, although this is generally linked to a file formatting problem.
If you are able to uncompress a complete copy locally, it can be uploaded to Galaxy that way. Try using a client such as FileZilla to manage the FTP, unless you are comfortable using the command-line.
Thanks for using Galaxy, Jen, Galaxy team