htmlsnapshot supports reporting error code for SnapUrl function. This can help you decide the problem of failing to snap certain pages.
It works like this:
The error code is an interger value which has following values:
0: The normal state.
1: The snapshot is successfully taken.
-1: Fail to take the snapshot of the page, check if your html image is too big to be fit into memory,
-2: Fail to save to file, check if you can write to the output image path
-3: Fail to open the URL. check network please
-4: Time is out before taking a snapshot, use a larger time out value or call SetForceSnap before snapping.