The server does not support downloading .7z files.

7-Zip is a compression software that claims to have the highest compression ratio today. It not only supports the unique 7z file format, but also supports a variety of other compression file formats, including ZIP, RAR, CAB, GZIP, BZIP2, and TAR. The compression ratio of this software is 30-50% higher than that of common ZIP files. Therefore, it can compress files compressed by WinZip 2-10%. File Extension: .7z. Currently, Windows server does not support the .7z format, so we need to set it.
IIS6 in win2003 does not support 7z by default. You need to manually add
Add the following content to the site --- properties --- HTTP header --- MIME type required in IIS:
Extension:. 7z (note that there is a point above)
MIME Type: application/octet-stream