It is very common error with .net assemblies. When someone included dlls from outside, in the project, this kind of exceptions are generic. Here is the resolution. Open the file location ( MySql.Data.dll in this case ) Right click on dll and check its properties ( it should not be encrypted and should have right access permissions ) Run the project after assigning appropriate permissions. It should work now. Even after this if it does not work. Check in web.config that assembly information is added under <compilation> tag. It is advisable to included new dlls using nuget package reference. It will update its reference automatically. Happy Coding!!!