Error in Tcl Script

Make sure nothing in your Quartus or Modelsim installation has spaces or any not a-z 0-9 characters in the name. I use C:\Altera for the install directory. Try that as some of the paths get very long which can mess up windows. Also, verify the md5 sum of all downloads. Seriously. Make sure you don't have an Anti-virus program that deletes or quarantines files. Something like that could explain it working at first and then failing. Check to see if rebooting your PC makes it work again.