Couple of things. VSTwain1.Capability = DeviceCapability.IBitDepth; gives a compile time error Cannot implicitly convert type 'Vintasoft.Twain.DeviceCapability' to 'int'. An explicit conversion exists (are you missing a cast?)
But when I run the above code it errors at VSTwain1.SetCap(); Error to Set Capability value at Vintasoft.Twain.VSTwain.SetCap()
Sorry for a delay. You already have received answer from our support team - you should change PixelType to Palette if you want to acquire palette images:
VSTwain1.PixelType = PixelType.Palette;
Best regards, Alexander