Unless you made arrangements to the contrary, the profile will be trying to use the credentials you are logged in to Windows with on the not-Mars machine to effect the network connection to Mars. As stated previously, you cannot connect (by any method) to the same server (Mars) from the same client (not-Mars) PC using two or more sets of credentials at the same time. Windows doesn't permit that. And you are already using Mars-based credentials to map S: so you cannot use not-Mars credentials to effect a UNC connection
You may be able to prevent this by adding the same Mars\username & password on Modify > Expert > Network (IOW, tell SE to use the same credentials as mapped-drive S is using).
It may also be necessary to toggle the 'try which first' setting on Network > Advanced. Sometimes Windows sulks if you try credentials it won't accept first, and it then won't immediately accept any others.
But mappings can be fussy about sharing with direct-UNC access, so you may either need to use S: in your profile or drop the mapping. Note that the mapped drive won't work on a Schedule (see para-2 here) unless (maybe) you are logged in at the time anyway. But using a UNC path (and storing the Mars credentials, etc) should mean it works on a Schedule
You may be able to prevent this by adding the same Mars\username & password on Modify > Expert > Network (IOW, tell SE to use the same credentials as mapped-drive S is using).
It may also be necessary to toggle the 'try which first' setting on Network > Advanced. Sometimes Windows sulks if you try credentials it won't accept first, and it then won't immediately accept any others.
But mappings can be fussy about sharing with direct-UNC access, so you may either need to use S: in your profile or drop the mapping. Note that the mapped drive won't work on a Schedule (see para-2 here) unless (maybe) you are logged in at the time anyway. But using a UNC path (and storing the Mars credentials, etc) should mean it works on a Schedule