An Entry Point Not Found error message might look rather weird (because you’re looking at the decorated name of a function).
but usually such an error just means that the wrong version of a DLL (in this case, OpenImageIO.dll) is being loaded by the main program (mayabatch in this case). The problem could be as simple as your PATH pointing to another application that ships a different version of the DLL.
Using Dependency Walker, you can check a DLL to see the decorated names of the functions it exports. But usually you don’t have to dig down to that level a detail. Dependency Walker will show you what version of the DLL is being loaded, and that’s usually enough.