Hi Vikash,
How many elements do you have in the DB?
Do you tried the manual discovery by command line?
nhDiscover -mode system,lanWan -c <community> -t 60 -ret 3 -o C:\outfile.txt -res C:\results.txt <ip address>
nhiDciMerge -i outfile.txt -o x.dci -commit no -Dm dci -Df dD
nhconfig -dciIn x.dci