I am getting this when install 

I tried to serach the following keys on other server but could not find it on other pgp key server

Err http://nebc.nerc.ac.uk unstable Release.gpg                 
  Unable to connect to nebc.nerc.ac.uk:http:
Ign http://nebc.nerc.ac.uk unstable Release                     
Ign http://nebc.nerc.ac.uk unstable/bio-linux TranslationIndex 
Err http://nebc.nerc.ac.uk unstable/bio-linux amd64 Packages   
  Unable to connect to nebc.nerc.ac.uk:http:
Err http://nebc.nerc.ac.uk unstable/bio-linux i386 Packages    
  Unable to connect to nebc.nerc.ac.uk:http:
Err http://nebc.nerc.ac.uk unstable/bio-linux Translation-en_US
  Unable to connect to nebc.nerc.ac.uk:http:
Err http://nebc.nerc.ac.uk unstable/bio-linux Translation-en   
  Unable to connect to nebc.nerc.ac.uk:http:
Ign http://downloads-distro.mongodb.org dist/10gen Translation-en
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
W: Failed to fetch http://nebc.nerc.ac.uk/bio-linux/dists/unstable/Release.gpg  Unable to connect to nebc.nerc.ac.uk:http:

W: Failed to fetch http://nebc.nerc.ac.uk/bio-linux/dists/unstable/bio-linux/binary-amd64/Packages  Unable to connect to nebc.nerc.ac.uk:http:

W: Failed to fetch http://nebc.nerc.ac.uk/bio-linux/dists/unstable/bio-linux/binary-i386/Packages  Unable to connect to nebc.nerc.ac.uk:http:

W: Failed to fetch http://nebc.nerc.ac.uk/bio-linux/dists/unstable/bio-linux/i18n/Translation-en_US  Unable to connect to nebc.nerc.ac.uk:http:

W: Failed to fetch http://nebc.nerc.ac.uk/bio-linux/dists/unstable/bio-linux/i18n/Translation-en  Unable to connect to nebc.nerc.ac.uk:http:

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Regards

Zeeshan Ali Shah
System Administrator - PDC HPC
PhD researcher (IT security)
Kungliga Tekniska Hogskolan
+46 8 790 9115
http://www.pdc.kth.se/members/zashah