Have you ever uploaded anything prior? If yes, how many files have you uploaded and what is the total size of all uploaded files?
Under manage, there is a setting that limits the total size of the files to be uploaded. If you exceed that limit, then that might explain the error that you received of not being able to upload.
Depending on your version, there is a way to determine how much data you have uploaded to see if u have exceeded the limit or not. If you are not an admin, you may need to check with them to see if you have exceeded the limit or not.
Another option would be to clean up some other uploaded files and retry your upload (assuming you have uploaded files previously).
Off the top of my head, i believe the default setting for total file size per user is set to 500mb. So if you are attempting to upload a file that is 550mb in size...it should fail. Likewise if you uploaded 10 files each that are 50mb in size and are attempting the 11th...that is gonna exceed the limit and fail.
Hope that helps.