Are there any big difference between built in groups (like, approvers, designer, Site Collection Resources members, owners, etc.) and custom groups (like I created using SP gui. Sales-Marketing, Sales-Approvers, Sales-VP)
I have "Anyone can view this group checked". I am trying to get all the users in a group so I am using this web services _vti_bin/UserGroup.asmx and GetUserCollectionFromGroup method. When I use Approvers or other build in group it works. If I use a custom group then I get error.