Problems with Sony Vegas HD project

I'm working on a short film project filmed in 720p HD with a Nikon D3100. I edited using a proxy system. I am now finished the editing and am trying to replace the proxy files with the HD ones and eventually render the project. I'm editing with Sony Vegas Movie Studio Platinum 9.

The problem is that I've replaced about one scene's worth (20-30 files)of clips, but now Vegas won't let me replace the other files, or I do replace them and it won't let me save. There are various reasons given: "Sony Vegas is not responding etc." , "Sony Vegas could not save ___.vf. The file could not be created.". Some times the program just freezes up and shuts down automatically.

I've researched this a lot and tried everything. I've shut off Avast! Antivirus, disabled Windows Defender, Superfetch and other unnecessary programs. I've increased the page file and made Sony Vegas' priority "High" in Task Manager. I've made the preview window in Vegas "Draft AUTO" and disabled "Waveforms and Frames".

Sometimes after Vegas closes down, the project file disappears completely, including the ".vf.bak" file. Luckily I made copies.

I've been working on these problems for almost a week. Any help would be greatly apreciated. My editing machine is a Sony VAIO laptop with 2gb RAM with Windows Vista 64bit.