As far as i know, the firmware with this version number has never been released officially from Nokia.
You had to upgrade the RX-51_2009SE_20.2010.36-2_PR_COMBINED_MR0_ARM.bin, latest from Nokia, to achieve this version RX-51_2009SE_21.2011.38-1_PR_COMBINED_MR0_ARM.bin.

On the downside, there is no official checksum for non-official packages to check integrity of the software. You know the risks... and so on. The upgrade from 20.2010.36.2 to 21.2011.38-1 is just downloading five to six security updates.