Lotus notes traveler error code 28

While I install a lotus notes traveler on android device, I got below messages.

The error code 28 is not on the lotus notes trouble shooing document. Could you please give me an advice for the error code means and how to solve it?

connecting…

Sync completed with errors.

Error: Unexpected error(28). Initial sync is not complete

Subject: reply to: Lotus notes traveler error code 28

This issue fixed after restart traveler server.