Here's a simpler fix. A sister program to pscp is psftp, which is interactive. The first time you run it from a command window, it gives you the fingerprint and...

I solve this problem by creating a named range in the spreadsheet and importing the named range instead of the worksheet.

I was mainly concerned about whether the single user login was contributing to the problem, since I couldn't find anything on that one way or the other.

There are many...

Use Alter Schema.

The explanation for the change is in BOL under the heading User-Schema Separation.