The rgn 49 value refers to a memory region within the GPS.

an interesting doc. about webupdater :
Usage: WebUpdater command line options:
<pathname> - Name of file to send to the unit
[/i] - WebUpdater should be run in installer mode.
[/k] - WebUpdater should keep running after a successful transfer.
[/autorun usb|serial] - WebUpdater should autodetect a USB or serial device and begin transfer immediately.
[/checksum_check rgn=<rgnnum> chk=<chksum>] - After transferring data to the region specified, WebUpdater will request the unit to checksum this region.
[/unlock_check fid=<familyid> pid=<productid>] - Before transferring data, WebUpdater will ensure that the user has unlock codes for the given family and product.
[/sacrifice_maps rgn=<rgnnum>] - WebUpdater will ask the unit if <rgnnum> is large enough for the data it will receive. If not, MapSource maps will be erased to make room.
[/offline path=<location of Package.XML>] - WebUpdater will perform the update using Package.XML instead of the Garmin server.
[/upload_file rgn=<rgnnum> path=<location of img file> -autorun usb|serial] - Performs image transfer.
[/offline path=<location of update files> -autorun usb|serial] - Performs all updates in the given folder.