The NET_DVR_Login_V40() function requires specific data types. Passing a string where an integer is expected, or using an ANSI string when Unicode is required, triggers Code 9.

To fix the problem, we first need to understand it.

: Because error 9 is a data reception failure, it often stems from the client requesting a stream that cannot reach it due to network settings, such as incorrect DNS configurations or firewall rules.

: A primary driver of this error is a mismatch between the version of the HCNetSDK.dll library and the device firmware. If the SDK is too old to support features in newer firmware (or vice versa), the data stream handshake fails.