appid becomes invalid

Hi - I am using the php geoplanet wrapper and developing an app. As far as I'm aware there is no way I'm hitting the 50K a day request limit.

However, my app starts processing my data and then, part way through, fails with: A valid appid parameter is required for this resource. The appid parameter has been valid for previous requests and then appears to become invalid.

Has anyone else seen this? Is it a known issue? Or have I just done something really stupid?!

Thanks for any suggestions!
Alex