hey guys~i'm currently doing web services in C# and i came across this error when i click on the invoke button on the page.

i am using a external DLL file which i created mysef. the dll itself uses an API of another software. i have added reference to the dll and copied the dll file into the bin folder of the web service. but this error still comes out when i test the function in the web service.

can anyone please help me~thanks alot!!!