Runitai Linden has released a pre-QA version of a modified viewer. The mesh upload function has been changed to solve some problems. The primary problem being SH-3055 – Cannot upload any model (*.dae) file; “xxx failed to upload, see the log file for details.”
Runitai announced the release in a comment in the JIRA.
REMEMBER: This is an untested build so it likely contains other unrelated bugs.
If you find problems with the viewer’s mesh upload, post the information in SH-3055. This should be a JIRA item open to all SL users.