Here is how I understand it. When you use Windows authentication to connect to SQL Server, SQL Server tries to pass those credentials on to the file server and...

Your problem could be what is referred to as the "Double hop" error: User logs into SQL with Windows Authentication.

File to import resides on network machine (UNC path)....

Have a look at http://www.sql-server-performance.com/faq/domain_error_occurred_p1.aspx

Try running your query with only the content of the SQRT i.e. power(3.0902,2)+4.0*num*(1-[current]) and see if you can identify the problem with yor data.