This error indicates that the "upload" directory under the web archive interface tree (that is, the "archives\upload" directory) does not have the NTFS file system permission "modify" set.  Under very old versions of the web interface, "read/write/execute" was sufficient, but newer versions of WA.EXE also require "modify" (which apparently is not implied by "write").  Setting the permissions accordingly should eliminate this error.  See also 2.12.