sqlagent task with interop excel

Hi,

I created a task with visual studio 2010 shell that performs the following steps:
-creation of an excel file
-import data using 'data flow task'
-protect the file with a password using 'script task', using c # and Microsoft.Office.Interop.Excel;
running the task from visual studio, all the steps are performed correctly;

performing the task with sqlagent does not run the script protection (returning this exception: the excel file is not found or is opened by an 'other program)
sqlagent runs as 'sa'

Any tips!!!

Thankss!!