We upgraded a existing working installation of Sugar 6.5 to Suite 7.7.9. We tested on a test server and everything seemed to work. We then backed up and tested our live server and things seemed to initially work, but within the first two days we began having problems, as well as running across a couple things that may not have been tested thoroughly.
Problem #1 Users that are not admins can’t access opportunities and cases. Some dashboard items only say ‘no data’.
Problem #2 When trying to edit opportunities or cases, the data shows up in a window that says something like ‘error page’, is plain without CSS, and at the bottom says “If this error persists, please have your administrator disable Ajax for this module”. So we disabled ajax on most pages and they appear to work…
Problem #3 No longer able to edit records. When trying to edit records (cases, opps, users, etc) after clicking Save, goes to an all blank page, no errors. after re-entering the main page, the data was not saved.
At this point we are about to pull the plug on the whole thing and lose a couple days of data, and go back to SugarCRM. Not sure what else to do.
Ubuntu 12.04LTS if that matters.
If it worked locally and then online (for the first days) then the software is fine.
Note: 7.7.9 its a too old version, actual version is 7.9.0
Did you make an Admin->Repair->Quick Repair and Rebuild ?
You need to verify your logs and permissions on system.
There are lots of topics here on permissions issues and permissions degradation over running your Scheduler jobs as root
Some Topics (not picked by most relevance but just so you can start:
https://suitecrm.com/forum/suitecrm-7-0-discussion/9901-undefined-error-on-pop-up-screen#33927
https://suitecrm.com/forum/installation-upgrade-help/10508-problem-wqith-user-interface-after-upgrading-to-7-7#35824
https://suitecrm.com/forum/installation-upgrade-help/3551-7-1-5-upgrade-fails-at-system-check-permissions-problem-with-log-files#21832
We seem to have found our main problem.
First a little background. We had trouble using the Sugar to SuiteCRM upgraders that were available and saw in some of the forums that you could install SuiteCRM, point it to the Sugar database, then run the “quick repair and rebuild” to update the database, so that’s what we did. This seemed to work on initial inspection, but apparently we didn’t do enough testing.
So once we started to run into problems, I took a look at the suitecrm.log file and discovered errors writing to the database. The repair and rebuild did add quite a few of the new tables, but there were still several tables missing, and some missing fields in existing tables. Since I had saved a copy of the database from the initial install of SuiteCRM, it was just a matter of comparing the two databases and adding the missing tables. After that things seemed to start functioning as expected.
You should have started by that “a little background” in your first post! It’s a very different thing to run the normal Upgrade process or try such a stunt! 
You should have a look at the upgrade scripts. Try unzipping the Upgrade package, and have a look at the scripts it runs. They do a lot of things, not just create tables.
This might give you clues to other things you will need to fix. I’m afraid there might be quite a few. SuiteCRM is a big application, and difficult to test.
Good luck!
With such a big upgrade we would recommend that your always do additional Repair & Rebuild after the upgrade but also, Repair Roles and Rebuild Relationships (a reason why admin users were not able to access certain modules and missing relationship tables). The Quick Repair & Rebuild is aptly name - it does a Quick Repair & Rebuild, but you would require additional rebuilding after a bigger upgrade.