PInvoke/Interop to access unmanaged code

I have a c# program which is using an unmanaged 3rd party dll to control a device. I am using the following code to access the dll:

[DllImport("3rdPartyInf.dll")]
public static extern uint Init([In]int par1, [Out] char[] param2, [Out] uint param3);
Now, the problem is that while this is fine for our desktop machines, it throws a DllNotFoundException - Unable to load DLL ("3rdPartyInf.dll") if I try to use a laptop (Dell Latitude D800). It makes no difference whether I try to access the dll from vc++ or from c# - even from vb!

All the machines are running XP SP2, .Net Framework 1.1, VS 2003 etc. I have checked the paths, .config files, hotfixes etc.

I can't debug into the error and am starting to run short of ideas, anyone else got any?!

Thanks.

[781 byte] By [Paul_G] at [2007-12-16]