Unable to connect to Orange cellular network with new iPad 4G

I recently traded in my iPad 2 for the new model and decided to buy one with 4G capability for when I am out of a wi-fi area. Bought my Orange micro SIM, activated it and checked that cellular network settings were correct. My iPad works beautifully on wi-fi, but when I try to connect to Safari or my mail using Orange, I get an error message saying it cannot connect to cellular network, despite the fact that I have 3 or 4 bars showing. My iPhone connects to Orange with no problem.
So far, I have reset network settings, double checked my cellular data settings and tried turning cellular network and the iPad off and on. Everything seems fine with the SIM.
Bearing in mind that this is my first time using cellular network on an iPad, could anyone give me an idea of what to try next?

Yes it's most likely due to you not being on an iPad tariff, I could not use my O2 sim in mine either, I'm not sure if the iPad is locked to three but I used a payg plan on 3 which is 1gb for £10, 3gb for £15 or I later got a pay monthly sim from three £15 for 10gb usage allowance. These companies screw us over as the unlimited Internet you get with your phone does not seem to work in an iPad. You should contact orange and ask for an iPad tariff. Hope this helps.

Look on eBay, you'll get 3G for 3 month at £13 with 3 network

I am on an iPad tariff - pay as you use with Orange. I rang them to double check having also checked my online account.
As everything was backed up on iCloud and to my iMac, I have just reset the iPad to factory settings and started again. Lo and behold, I can now connect to the cellular network. Early days yet, but it seems to switch perfectly between cellular and wi-fi at the moment. Fingers crossed that it continues.
So none the wiser about why it wouldn't do it before, but I'm not complaining.
Thanks for the help.