Error 500: The template is updated in other place. Please reload the original page and retry it again

When I edited my layout in Blogger and tried to preview it, I used to get the following error:

The template is updated in other place. Please reload the original page and retry it again

Then when i tried to save the layout, I used to get this error

The server was unable to save the form at this time. Please try again

After searching a lot on google, I found out that adding mobile only widgets causes this problem.
So, I followed the following steps to fix the issue.

Go to Template -> Edit HTML

Then search for mobile="only". You might find something like this:

<b:widget id='HTML4' locked='false' mobile='only' title='Mobile ad' type='HTML'>

Change this to:

<b:widget id='HTML4' locked='false' mobile='yes' title='Mobile ad' type='HTML'>


This will solve the problem. I think google should do something regarding this problem as it is not that straightforward to fix this.