How to reproduce the issue:
- Login to your Joomla 2.5 installation as administrative user,
- Click on the "Configuration" menu item.
- Page with common styling is loaded
- Page loads partially
- No css files load. Page is bare black and white unstyled layout
- At the bottom of the page you can see the following error message: "Fatal error: Class JDatabase MSSQL contains 22 abstract methods and must therefore be declared abstract or implement the remaining methods" plus the full path to the file.
Why does it happen?
- One of the extensions that you've installed had put files in the joomla core folders that are used to connect to databases other than mysql (MS SQL, MS Access or Oracle)
How can I fix it?
- To fix it go to the folder that is indicated in the error message (ex: /home/username/domains/yourdomain.com/public_html/libraries/joomla/database/database) and move the file from the error message out of the folder. Do not rename it but move it to your PC (for backup just in case) and delete it from the joomla folder.
- Reload the page.
- Page is likely to throw error again but this time with a different file name.
- Delete the files mentioned in the error messages until the page loads without issues.
What are the likely filenames that I have to delete?
But you should still read what your error messages report.