Hello Ejaz,
There is a KnowledgeBase entry on the Measure Support webpage that addresses this very issue. I went to the Measure support webpage (http://www.ni.com/support/meassupp.htm) and saw a link entitled "Non-Technical Measure Issues" that gives the contact information for the NI Sales Department, which handles issues like lost serial numbers. I recommend you visit the Measure Support site for more information.
As far as I know, neither of the numbers you gave in your posting are serial numbers...the 800265B-01 number is probably the part number for the Measure shipping package, and the 500277D-00 is probably the part number for the Measure CD.
Good luck, and have a nice day.
Darren