.NET Assembly.LoadFrom slower when PC is on a particular network

I have a .NET 3.5 C# app that loads plugins and searches for items using:

var myAssembly = Assembly.LoadFrom(c:\...\MyPlugin.dll)
Type [] Types = myAssembly.GetTypes();

When the PC is disconnected from or on most networks, these commands complete in milliseconds. But when the PC is connected to a particular user's network, they take 30 seconds each. How could a network cause these command to run more slowly when loading the same local file?

Thanks in advance for any thoughts you have.