To find out about how/why of blocked extensions read
this post 
Possibilities to unblock are:
File Extension Unblocker
A-Patch
Mess Patch 7.0.0777
SPNG (Msg Plus! required)
Please note that these filetypes were blocked in order to counter the propagation of viruses over the .NET Messenger network. Always be wary of any file you receive!
Advice: Scan the files you receive with a good AV program (also make sure the virusdefinitions are up to date) after receiving first. You can set MSNM to do that: tools > options > file transfer
Note to helpers: Please post full info, no direct downloadlinks. There may be some things the person needing help might want/need to read first.
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