I couldn't find a compiled 64-bit version for windows so I downloaded the source and compiled both the 32 bit and 64 bit versions:
lzo-net is an existing sourceforge project that wraps the C LZO dll however it is very outdated - the lzo version in that project points at v1.08 and the latest is 2.06. That project is a single class
LZOCompressor which handles the calls between your application and the C LZO library.*
I added/fixed a few things as
LZOCompressor no longer worked with v2.06 of the LZO C libraries:
DllImport attributes needed fixing when calling from .NET 4
2) String memory cleanup issue
3) Added feature: Detects 32bit or 64bit and loads the correct C LZO dll.
How to use in your .NET Application
A sample C# Application is available to download (838kb) which demonstrates using LZO from within either a 32bit or 64bit C# Application. This download is larger than you might expect because LZO C now depends on the VC++ Redistributable library
msvcr100.dll which I've included in the download.
*I've emailed the owner of this project but haven't heard back as yet
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