WindowsServer 2008 not searching DLL in PATH Environment variable at runtime

I'm experiencing a problem with Windows Server 2008 when running Unit Tests with Nunit.

Basically, In a Windows 7 machine I'm able to execute my Unit-Tests by following those steps:

1. I open a VS10 command prompt
2. I execute a bat script for adding to the PATH env. variable, some additional folders where my assembly (that contains unit-tets) can find additional DLL required at run-time. My assembly is not located in the same folder where some required DLLs are placed.
3. I run nunit-console (2.6.4) and it's able to execute the Unit Tests that are contained in my assembly.

In a Windows Server machine (2008 r2), I follow the steps listed above, but I'm not able to run unit-tests because It seems that Windows is not loading the required DLL from the additional folders I configured in the PATH env variable. I tried also to change the PATH env variable globally for adding the additional folders, but it seems that the required DLL are not loaded from the PATH when nunit-console has been executed.

Are you aware of some limitation in Windows Server? Do you know any work-around?

Thanks in advance.