OneDrive for Business doesn't sync - solved.

Is your OneDrive folder not syncing anymore? Do you get sync errors that won't go away? Do all of the files in the sync folder have a red X on them? If so - here are the answers.

Sometimes you copy a large amount of data into your OneDrive sync folder or you make a drastic change in the folder structure (taking all of the main folders and putting them into one subfolder, for example) - this may lead to major sync problems.

What doesn't work:

Stopping - restarting sync, syncing a new folder, deleting everything in your sync folder and then hoping it would resync, deleting everything on the server and hoping it would resync from your pc folder, running the "repair" function of the OneDrive desktop software, uninstalling and reinstalling OneDrive.

If you've done all of the above and still no luck, read on.
The only solution I've found so far is doing the procedure below (recommended by MS support team) and it actually works.

Important! Make sure that your server-side copy of your files is up to date, because you will lose all of the local data from your computer's Sync folder and your computer will then resync from the server.
If it's not up to date, then backup the data in your sync folder, just in case.

1. Right click on the Windows status bar, select Start Task Manager, and get a list of running processes as follows:
If you’re running Windows 7: Select the Processes tab.If you’re running Windows 8: Select More Details in the bottom left and then select the Details tab.

2. Verify that none of the following processes are running:
groove.exe
msosync.exe
msouc.exe
winword.exe
excel.exe
powerpnt.exe

3. If any of the above processes are running, stop the process by right-clicking it and selecting End Process.

4. Give yourself an administrator role as follows:If you’re running Windows 7: Click the start button and type cmd in the search bar. When cmd.exe appears in the results, right-click it and select Run as Administrator.If you’re running Windows 8: Drag your mouse to the bottom left corner of the screen, right click on the Start icon that appears, and then select Command Prompt (Admin).

5. At the command prompt, delete the Office file cache and Spw folders by issuing four commands as follows:
a. Type this and then press the Enter key:
cd %USERPROFILE%\AppData\Local\Microsoft\Office\15.0\ 
b. Type this and then press the Enter key:
rmdir OfficeFileCache /s 
c. Type this and then press the Enter key:
cd %USERPROFILE%\AppData\Local\Microsoft\Office\  
d. Type this and then press the Enter key:
rmdir Spw /s

6. If you get an error when executing either rmdir command (steps b or d), one of the .exe processes is probably still running. Correct the problem by returning to the Task Manager (step 2), stopping the processes, and then removing the directories as described previously.

7. Start the OneDrive for Business client and re-sync the library.