I'll presume that all three cameras are in similar settings, so the IR strength is a true apples-to-apples comparison. If not, try placing the problematic DCS-942L in the same room as one of the other DCS-942Ls that's working well. Open the web UI for two DCS-942Ls (problem camera + one of your other two) and perform a side-by-side comparison of all of the settings. If all the settings are identical, then call D-Link technical support, and try to get an RMA.