Problem with Socket in c++ 6.0 (I have no choice and have to work on this version of the language) and what am I doing wrong?

Question

C++ / C#

There is a Socket through which communication with an external device takes place, it responds. To constantly poll the device, a thread is created, otherwise a deadlock occurs when it is polled. A message is sent beforehand to start sending data. When polled by the recv command on a given stream, the return value of the message being read is 0xffff instead of 5. To clarify, the commands for working with the socket and all work with it takes place only in dll (this is a requirement). In other situations, everything works. The thread is created in the program interface and functions from the dll are called (in other languages, this trick worked, only functions not from the dll were called). Do I need to create this thread in a dll, or can I call functions from the thread and then return the resulting values ​​to the main thread? Just encountered this for the first time.