Just a couple of SWAGs:
One would think that a factory reset will leave this value in the correct state, but if you can log into the OBi via it's IP address, look at the System Management page, under Auto Provisioning, and ensure that ITSP Provisioning Method is set to "System Start". IF you have followed any advice on a forum to disable ports or otherwise block access by OBiTALK to your device, it won't be able to see it to add it to the portal.
This is a long shot, since I haven't used a managed service provider, but if you previously gave control of your device to Vestalink as a managed service provider, you won't be able to configure it until they release it (delete it from their provisioning system). This same behavior can be seen if the device was previously assigned to some other OBiTALK account, and that account still "owns" the device on it's portal dashboard: it needs to be deleted from any other account before it can be added.
*note: don't attempt to use Google Chrome Browser to locally configure your OBi at this time. A recent software update to Chrome is preventing the OBi's embedded web server from displaying frames of settings. Use Firefox, MSIE or Safari instead.