if you have a lot of reports to use you need the SSRS Scripter
. I remember it being easy to use, but that was a year or two ago. I think you give it a source and destination, and then select the folders you want to move and it does it for you. fabulous tool. I hope I provided the right link
I just took a look at the tool you were using and it looks almost identical to the one I used. if you have auth problems with one tool you may have the same problem with any tool you try.
SSRS has it's own level of security on top of the db security. you may have to add sa to the ssrs administators. I'd try a different account. I'm not up on my best practices but I'm sure adding SA to SSRS administrators isn't one.
you add this via the report manager, site settings, security.