I recently setup a new CRM Online environment to implement the Grants Management Solution Accelerator.
After completing the deployment I logged in to test the solution and ensure everything was working as expected since we plan to use this for a demo in the near future. There were several items that required some attention like names used for some of the views, JavaScript errors, etc.
In addition to the issues above, I ran into a ribbon display issue on the Incident entity. This error was a little more tricky to resolve since there was no JavaScript on the form. I thought maybe there was some form corruption so my first step was to create a new form but unfortunately, that form also would not display the Ribbon. I also tried opening the form in various browsers to rule out a caching issue, but, quoting the infamous Soup Nazi from Seinfeld, No Soup for Me.
At that point I decided I needed a little more information so I hit the magic F12 button on my keyboard, selected the Script tab and found the issue.
I started by Binging “unable to get value of the property “style” but didn’t come up with anything useful (also tried Google 
with same result) so I decided to Bing the file name that was having the issue, “form.js?ver=”, and I found the solution.
“A script error occurs or the ribbon fails to load in the Case, Product, or Service Appointment entities in Microsoft Dynamics CRM Online or after applying Update Rollup 12 in On Premise”
KB Article 2807519 has the fix which is to check the Expand by Default property of the forms assistant or uncheck Enable Forms Assistant in the property of the form.
Following are some of the errors you might encounter when experiencing this issue:
SCRIPT5007: Unable to get value of the property ‘focusin’: object is null or undefined
global.ashx?ver=-505927664, line 5 character 58707
SEC7115: :visited and :link styles can only differ by color. Some styles were not applied to :visited.
main.aspx?etc=112&extraqs=%3fetc%3d112%26pagemode%3diframe%26preloadcache%3d1360353202171&pagetype=entityrecord
SCRIPT5007: Unable to get value of the property ‘SubjectClicked’: object is null or undefined
main.aspx?etc=112&extraqs=%3fetc%3d112%26pagemode%3diframe%26preloadcache%3d1360353202171&pagetype=entityrecord, line 549 character 131
SCRIPT5007: Unable to get value of the property ‘style’: object is null or undefined
form.js?ver=-505927664, line 1 character 22102
Cheers
