Are you finding io.dll just press download button to get your io.dll file.
If some software in your windows OS wants io.dll your operating system will ask for DLL file. When that DLL file is not available you will get this error.
If you have moved your file or changed the name of dll file you will get this error.
You will mostly see there errors when you dll file is missing:
If you need io.dll Download it right now and install it into your system to fix the error as soon as possible. just Install io.dll and fix your error.