First Slice demo won't back up

[Document]

I have Portal: First Slice downloaded. I go to Library and right-click "Portal: First Slice" in the navigation menu. I select "Backup Game Files". I click Next in the dialog box. I accept the default path (c:\games\steam\Backups). The dialog box says "Disk space required: 3608 MB / Disk space Available: 44300 MB". I click Next twice. The next stage of the dialog says "Backing up Portal First Slice". So far, so good, but then nothing happens. The "Time remaining:" field remains blank. The progress bar remains empty. The progress meter reads "0 / 0 MB".

I haven't had any trouble backing up other games. Has anyone else experienced this? Can anyone try it and see if the same thing happens? Does anyone know of any possible solutions?

[cetjunior]

I have the same problem. Anyone got the solution?