GetDeviceListSerial returns empty string as serialnumber

I am using Frontpanel 4.0.8 under Windows 7. I connect to the xem3010 using the csharp library. I built my code on the basis of the provided examples (mostly pipeTest and DES). As i am still developing my design i am often reprogramming the opalkellyboard, I am doing this fully automated using the csharp library, similar to the DESexample. However once in a while okCFrontPanel m_dev.GetDeviceCount() returns 1 (so it finds the Opalkelly), but m_dev.GetDeviceListSerial(0) returns an empty String ā€œā€. If this happens once it will again, until i unplug and plug the OpalKellyBoard.

Any leads to what iā€™m doing wrong?