That indicates another program is using a network port. If you can’t find the program and kill it by hand probably just rebooting your computer is the easiest.
It seems that you run multiple Slicer executables at the same time, which use the same resources (network ports, database files, etc). This leads to inability to delete the database (the file is open in anther instance) inability to start another listening server on the same port (you can probably ignore this error, as the other instance receives any sent DICOM data), etc. The easiest way to resolve any potential problems is to run only one Slicer instance at a time.
Do you get any error messages on screen?
Do you see any error messages in the application log?
In DICOM module / DICOM database settings, does “Remove unavailable data sets” remove the non-loadable patients?