dll not found exception when c++ methods are call from multiple threads

Hi, I have few c++ dll methods being called from my c# script. When I call the methods from main thread they work fine. But when I call the methods simultaneously from multiple threads I get "dll not found" exception. I am using normal c# threads. And in those threads I am not calling any Unity functions. Sometimes I get garbage exceptions too. The c++ methods are thread safe. Thanks and I appreciate any help.