CSS Mismatch - Portal 7.01 and Backend 7.21

Hi Experts,

We have been getting a CSS mismatch popup afther we upgraded the Backend system to a higher level than the Portal.

Whe get the following popup message:

I have been looking for a solution for quite a while now but I don't see a direct solution besides upgrade the portal.

Unfortunately upgrading the portal is, for now, not a option since we are upgrade all the Backend system to 7.21.

There is one way to change all the iViews to force the use of the Backend CSS (Hand over Portal Stylesheet / and UR|Is parameters) .

But since we use a lot of iViews it will be a quite time consuming and delicate work.

Has anyone a good solution to hide the popup, temporary.

Thanks in advance,

Arnaud