I ran into this particular issue a while back when someone used SharePoint Designer to modify a page based on the default design template. This is the blog post I found that covered the issue as well as any other:
http://ranaictiu-technicalblog.blogspot.com/2010/05/sharepoint-2010-current-page-has-been.html
Sohel ran into the same problem that I did… the two solutions you can use end up having other side effects that aren’t very desirable in many situations. You end up making a fix for this problem message, and then you have to make another fix to fix the side effect, and so on and so on. Pretty soon you’re building a house of cards made up of band-aids over band-aids.
My point here isn’t so much on how to fix this problem. Instead, it’s an observation that at times it’s best to tell the business customer “it’s not worth it to make that modification you wanted.” In my case, they tweaked the page to remove something they “didn’t like”. It wasn’t something that was broken… they just didn’t like that the page used certain wording.
At times I long for the days of large mainframe green screen applications where people had to use what was put in front of them. Application development these days allows everyone to have an opinion of what’s “good” or “bad”, “right” or “wrong”. Unfortunately, all opinions are not created equal, and telling me you showed it to your sister and she didn’t understand it is not a valid reason to get whatever changes you want.
SharePoint Duffbert 
This happened to me when I tried to add CSS. Rather than hide this status bar, you can add a CSS path in the master.page and this fizes the problem.
Below line 19:
Add this 20 line:
This happened to me when I tried to add CSS. Rather than hide this status bar, you can add a CSS path in the master.page and this fizes the problem.
Below line 19: *
Add this 20 line:
*
Good advice thanks for sharing your experience about this. I am getting same message on a SharePoint online page and I am afraid to revert it as the person who changed it retired.