Hi,
Just try connecting through telnet and give a try by giving session ips.... I guess some problem through getting that through console.
Or just check if the IPS module package is there in the disk.
ASA#dir disk0:
the package should be something like this IPS-SSP_5515-K9-sys-1.1-a-7.1-4-E4.aip when you execute the command.
You can refer the below document for further help in case if the issue not solved.
http://www.cisco.com/en/US/docs/security/asa/asa84/configuration/guide/modules_ips.pdf
Please do rate if the given information helps.
By
Karthik