I tried to serach the following keys on other server but could not find it on other pgp key server
  Unable to connect to nebc.nerc.ac.uk:http:
  Unable to connect to nebc.nerc.ac.uk:http:
  Unable to connect to nebc.nerc.ac.uk:http:
  Unable to connect to nebc.nerc.ac.uk:http:
  Unable to connect to nebc.nerc.ac.uk:http:
Fetched 316 B in 3s (99 B/s)                                   
W: There is no public key available for the following key IDs:
3B4FE6ACC0B21F32
W: GPG error: 
http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 759A8E0E5BA15160
W: There is no public key available for the following key IDs:
3B4FE6ACC0B21F32
W: There is no public key available for the following key IDs:
3B4FE6ACC0B21F32
-- 
Regards
Zeeshan Ali Shah
System Administrator - PDC HPC
PhD researcher (IT security)
Kungliga Tekniska Hogskolan
+46 8 790 9115