sync: call failed: 1 (zumero:http_500)

[sudo-s14]

I am using this sample to check syncing mechanism, on one iOS device, with a simulator.
I signed up with Cloud Hosted network and i Got the following Data:
// SELECT zumero_sync ('main',
// 'a Url',
// 'mydbfile',
// zumero_internal_auth_scheme('zumero_users_admin'),
// 'admin',
// '1234');

On the iOS Device, it works fine until I run the app again from xcode. After running again, it give me the following error
"sync: call failed: 1 (zumero:http_500)"
And when i tried this on the iOS Simulator it shows again this above error.

Please suggest me.
Thanks
Shameem Ahamad