The Hosted environment will use Windows authentication and the name set in Dimensions when a user is added must match what Windows is providing, if not there will be a mismatch and the user will not be found in Dimensions.
To resolve this issue:
Log into the Gateway as the Hosting Admin user
Launch Dimensions
Click System, User Records
Select the user having the issue.
Check that the user's Name field shows as CLOUD\<username>. In this case, nearly all user names follow the format: DM????F.SSSSSS where ???? is replaced with the same number everyone uses, F is the user's initial, then a full stop followed directly by their surname.
If the name needs to be changed, click Edit.
Amend the name.
Click Save.
Ask the user to retry Launching Dimensions and logging in.