After 250 measurements, the flow cell reaches its usage limit and is automatically locked. This limit is set to guarantee the factory calibration of the flow cell.
In other words, it does not detect the flow cell at all.
Press down on the flow cell to ensure that is properly in place. Press down hard to be sure.
You hear two clicks during flow cell installation. Afterwards, it should just feel slightly springy when you press the center part of the flow cell (no more click sounds).
If the issue persists, then this is a hardware issue with your flow cell or your BactoBox® setup. Contact our support team to discuss the matter further.