Recently at one of our customer sites, we were running in to issues with downloading large files from MOSS Windows Explorer View. Users had been able to upload a large file to a SharePoint document library using the upload file features of a Document Library. However, when trying to download the same file using Windows Explorer view, they were getting errors. NOTE: They could still download the same file using right-click save-as option or the send to menu on a file in the document library.

Upong opening a case with Microsoft, we found that it is because during download from a Windows Explorer view, the protocol that is being used required a "Contiguous" chunk of memory that is twice the size of the file that is being downloaded. On a 32-bit OS, there is a limit of 2GB per application pool. Our application pools were always running around 700MB or so and hence after that for some reason, it was not able to find a contiguous chunk of memory that might be about 500 MB or so (Large files 200MB or more). This would cause downloads to fail.

Microsoft has mentioned this to be dependant on how the code was writtten and would possibly be fixed with the next version of SharePoint. Unfortunately, there is no immediate fix available.

The only option that they have suggested at this point is to migrate to a 64-bit OS and maybe 64-bit MOSS.

Not sure how it is going to work out, but hopefully this information helps someone.

Cheers,
Nilaish