Arduino IDE

When I open the Arduino IDE after a short while “unknown protocol: c” displayed in black box in bottom.
There is no issue from it to upload or compile. But always it shows that message. Please tell me what’s the meaning of that and what is the reason for this. I have uninstall and install the IDE, download the zip and run it. All the times it shows that error when I open the IDE
Please Help me

Have you tried searching the forum for the message in case other have the same problem ?

ChamodAbeywickrama:
When I open the Arduino IDE after a short while "unknown protocol: c" displayed in black box in bottom.
There is no issue from it to upload or compile. But always it shows that message. Please tell me what's the meaning of that and what is the reason for this. I have uninstall and install the IDE, download the zip and run it. All the times it shows that error when I open the IDE
Please Help me

So, you open the IDE, and let it sit there for a few moments and then that message pops up, correct?

When the Arduino IDE is opened it checks for updates, if you change the preferences option to check for updates at startup, does the message still show up? Which should lead you in the direction to troubleshoot.

Have you added the json urls for any other board/library packages? If so, check those fields for typos and stray characters.

DrAzzy has the correct answer. The problem is that you have something wrong in File > Preferences > Additional Boards Manager URLs. It sounds like you added a filename starting with c:\ to that field instead of a URL.

Thanks all. The problem was in additional board manager URL.

VS code arduino extension had added the sketch book location to additional board manager URL because the arduino.additionalUrls property in settings.json file of VS code had set to my sketchbook location. But actually I didn't set it to that location with my concern. However I empty the arduino.additionalUrls property in settings.json file of VS code and removed that folder path from arduino IDE preferences. Then problem solved.

Thanks All