Check the file on your 10.1.185.2 ftp server.
The above output shows that is downloaded a 7893K file which is too small for the WS-SVC-IDSM2-K9-sys-1.1-a-5.1-1.bin.gz file.
Look at he download page for the WS-SVC-IDSM2-K9-sys-1.1-a-5.1-1.bin.gz file:
http://www.cisco.com/cgi-bin/tablebuild.pl/ips5-cat6500-idsm2-sys
You will see that the file should be 23369742 bytes (22822K approximately).
So it looks like the file on your ftp server is incomplete if it is only 7893K.
You would need to download the file again from CCO and place it in your 10.1.185.2 ftp server. Once it is on your ftp server you will want to compare the file size against the file size listed on CCO to ensure you have the complete file before you even attempt the imahe installation.
If I remember right there had been a problem before where downloading the file using Internet Explorer would sometimes cause an issue. Internet Explorer itself would attempt to unzip the file because of the gz file extension, and you would wind up with a corrupted file.
If you do run into this issue then try using a different browser (like Mozilla).
This problem was only seen with the IDSM-2 System Images because of the .gz extension on the filename. All other files (like major, minor, and signature updates, as well as system images for other systems) end in either a .pkg or .img extenstion and so are not corrupted by Internet Explorer during download.
