1. An IP address conflict with the Digi device and another device on the network can cause this issue. There are several ways to troubleshoot this. For example, if the Digi device is configured with a Static IP address, issue the "arp -a" command from a Windows command prompt. Is the MAC address that of the Digi device or something else? You could also disconnect the network cable from the Digi device and then try to ping the Digi device's IP address. If you still get ping replies, it must be from some other device.
2. Go to Device Manager / Multi-port serial adapters / Advanced tab / Properties button. Select the 1st COM port, click the Change button for Port Network Profile, select "TCP: Less Overhead", check "Apply New Profile to Device and All Ports", click OK 3 times.
Note: This is generally suggested for WAN and "Internet Cloud" network environments.
3. Go to Device Manager / Multi-port serial adapters / Advanced tab / Properties button. Select the 1st COM port, go to the TCP tab, check "Complete Write Requests Immediately", click OK 2 times.
Unable to open one or more COM Port Numbers:
Assuming that the RealPort Connection Status described above says "Connected", you should be able to open any of the Digi Device's COM Port Numbers from the intended software application (related to the attached serial device).
If this doesn't work, try to initially narrow down the issue. For example, does the issue only happen with a certain software application or any software application? Trying to open the COM Port Number(s) in question with a terminal program like HyperTerminal and PuTTY will provide more data points. If those applications don't work, it's likely that other applications will not work either.
When using a terminal program for troubleshooting, ensure that the related COM Port Number(s) aren't already open by another program, as a COM port may be opened by only one program at a time. If you go to Device Manager / Multi-port serial adapters / Advanced tab / Properties button then select the COM Port in question on the left, note the Port Status at the bottom-right.
If Local COM is "Closed", it means no program has that particular COM Port Open at that particular point in time. This would be a good time to try to open that COM port with a terminal program.
If Local COM is "Open", it means a program has that COM Port Open at that particular point in time, and the program's name (putty.exe for example) should be displayed immediately underneath.
If you're still unable to open certain COM Port Numbers, try to rule out COM port conflicts. In other words, ensure that the Digi Device's COM Port Numbers aren't conflicting with another existing COM port number, for example from a Modem that's installed on COM 3.