After a long delay, Nuget packages for 2.0.13-beta1 are finally available!
Since they are beta, you will need to use a command line parameter when installing this package.
According to Nuget, you will need to use the following command:
PM> Install-Package Npgsql -Pre
Please, give it a try and let me know if it works ok.
This package also fixes the problem of police files compiled to .Net 2.0 framework only. This was giving problems when installing Npgsql on .net 4.0 runtimes. Thanks Yusuke Fujiwara for fixing it.