The extra slash is from Linux putting an escape character in the path, and is normal.
Personally, I've noted that mount.cifs has issues with long paths. The command wants to mount an actual share, and struggles when you bury the share path. If (in your example) the share is \\abc-server.domain.com\ABC, that's where you should be putting the upgrade folders.
Otherwise, create a share at the SolarWindsLEMv6Upgrade level, so you can tell the upgrade mount \\abc-server.domain.com\SolarWindsLEMv6Upgrade
The error 13 suggests that you've got a bad username/password, but that could be compounded by the long path.
The LEM's upgrade script is going to mount the share that you specify, and then look for the folders Trigeo and Upgrade, so make sure your share has that structure as well. When you're done upgrading, you can drop the LEM folder from the connector update in the same share and then upgrade the connectors too!
SolarWinds Knowledge Base :: How to apply a LEM connector update package