Hi Archie, before making any changes, as I opened the AdvancedHMI.exe file, everything was working fine, properly communicating with PLC.
I wanted to change the name of one of the Panel Meter. I closed everything and opened the Opened AdvancedHMI35v.sln. From there, opened MainForm.Designer.vb. Just changed the name of the Digital Panel meter (no other changes), and hit "Start" play button to see that name change was right. Closed AdvancedHMI35.sln.
Again, Opened AdvancedHNI.exe from bin folder, as I did originally. Now, I see that HMI does not communicate with PLC (getting failed to write value message).I also see that Tx/Rx Led ON USB-1761-CBL-PM02 blinks. That means it is connected to HMI. Normally, when HMI communicates with PLC, the Red Led blinks rapidly.