I have no idea what's going on, but:
1. When it fails, if you view the digit map setting in the OBi web interface, is it truncated? If so, you can determine the maximum length.
2. If the limit is on a particular string, rather than total storage, you could put a section of the map into each of several User Defined Digit Maps, then reference those from the Line Digit Map.
3. If you can't get that to work, including only the area codes you call the most will probably account for >95% of traffic, so it wouldn't cost significantly more.
4. Though cost would be higher, simply using an inexpensive VoIP provider for outbound calls would give you some advantages: higher quality (you'd eliminate two stages of gratuitous A/D and D/A conversion, eliminate the compression codec if calling other than a cell phone, likely have lower latency), much faster setup time, and the ability to have concurrent calls (assuming that you have another SIP device). If you are a heavy user, take a look at Voxbeam (premium route), US$0.0025/min. to most Canadian destinations.