You may be running in to an issue caused by Internet Explorer.
Internet Explorer, Tools, Internet Option, Security, Custom.
Find the "Include local directory path when uploading files to a server"
Click on "Enable"
Upload a new assett and see if the problem persists.
Also here is a link to the Compatibility Information for DMS.
As a general rule of thumb use:
Firefox for the DMM, SNS, DMP, MXE
Internet Explorer for the TCS, AS series encoders.