Sorry to bring an old thread back from the dead, but I just ran into this exact issue!
My newly created viewports were comining up with the number of -1. After doing a zoom extents on the new layout (prior to creating the new viewports), the viewports are numbered properly and I no longer get an error!!
Thanks for figuring this out bikelink!
Log into access your profile, ask and answer questions, share ideas and more. Haven't signed up yet? Register