The behaviour is due to the way that the Quantum CPU communicates to the NOE over the backplane during programming with any PLC programming software package.
When the PLC programming software (i,e., ProWORX,32, etc.) is connected to the PLC via the NOE, the CPU opens a seperate internal programming path to connect the NOE to the CPU. The programming information is passed on to the CPU directly from the NOE independent of the physical connection.
When the connection is broken while ProWORX is connected to the PLC, the CPU does not know that the physical connection to ProWORX has been lost. Since only one programming path can be opened to the PLC at any given time, any attempt to reconnect via the NOE is rejected by the CPU. However, if the NOE is lifted off of the backplane and is reseated, the CPU detects a broken connection to the NOE and resets the programming path. Furthermore, if you are able to access the NOE webpage, you can also double click on the PLC graphic and force all users offline.
This problem has been fixed in
Executive Firmware version 3.6 for the 140NOE77101
Executive Firmware version 3.5 for the 140NOE77111
Executive Firmware version 3.4 for the 140NOE77100
Note: 140NOE77110 is considered to be obsolete and has been replaced by the 140NOE77111