I cannot get any credentials to work in my subscriptions's properties for the section:

Credentials used to access the file share

http://www.webfound.net/fileshare_credentials.jpg

I tried putting in the credentials I used for the datasouce behind the report that this subscription is based on and as soon as I click OK I get:

An internal error occurred on the report server. See the error log for more details. (rsInternalError)Get Online Help

For more information about this error navigate to the report server on the local server machine, or enable remote errors