Upgraded from DNN 6.2.9 to DNN 7.3.3 Cannot Add New Pages from Control Panel

Any Ideas how to fix this?

I just upgraded a DNN site on our (test server 2012 running IIS 8+ and SQL 2012) from DNN 6.2.9 to DNN 7.3.3 and everything went fine. With ONE HUGE EXCEPTION.

Web Admin User cannot ADD NEW PAGES from Control Panel in DNN 7.3.3 after the upgrade.
Here is what happens in detail, when we click the control panel menu dropdown the under Pages>Add New Page, We get the normal entry fields for adding the page in the modal popup. After info is entered, we click "Add Page" only to find out that we get a white blank screen within the pop up modal where the page is being added.  Nothing else happens.

Next we close the screen only to find that the page does show up in the menu except when you click on it you get "404 Page cannot be found. 

As a further test we tried adding a page through the "Page Management" Console and to our surprise, we successfully were able to add a page with absolutely no problem. 

Basically our ISSUE IS:
1) Web Admin CANNOT add new pages from Control Bar.
2) Web Admin CAN add pages from Page Management console.

Can we have some suggestions on how or what can be done to fix this annoying surprise issue of not having the ability to add pages via the Control Bar? Is this a BUG in DNN 7.3.3? Or does anyone recommend another previous DNN stable version?
NOTE: When we review the event viewer, to check for possible recorded Errors, we find no errors are recorded.

Please advise as we have had to put on HOLD further DNN site upgrades.

Hello, Thanks for your reply,

Glad i'm not the only one who has seen this one.

Yes, I have checked the DNN Event Viewer and interestingly did not find any errors listed. Continued to adding test pages but not finding any General Exceptions in regards to time outs. To be on the safe side, i checked my web.config to make sure Event validation is still happening and it is still set to true (enableEventValidation="true")

But do not see any DNN Event Viewer errors in regards to time out issue. Perhaps I am looking in the wrong place?
Its very possible that this is a Time Out issue. Luckily I am testing on a Test Server so if you would like me to try any special script I'm ok with trying it.

Open to trying just about anything right now....

Kind Regards,

Thank you also Sebastian for the recommendation, However... after installing the Advanced Control Panel from www.oliverhine.com and testing it thoroughly, I still get the same issue. Adding a new page from his control panel still produces the same problem and does not resolve itself.

Working with DNN since 2004, have seen many strange things happen with upgrades, I guess this is my first time ever running in to this type of issue with adding pages from control panel.