Here is my pseudo-query:

SELECT row_guid FROM table

What should come back is this:

DAD26152-1C43-11DD-BD0B-0800200C9A66

Have you sent the actual SQL query (as implemented in your script) using some other DB client, and made sure that it returns the string that you say you should be getting?

Have you looked at the table definition to determine what sort of data field you are querying for? (Does the DB server happen to provide some "special" data type, is the field encrypted, might there be some DB-side function call that should be used in the query string to fetch the value correctly, etc?)

I don't think we can say anything useful based on the information originally posted (unless someone else has actually seen something very similar...)