One possibility is that you did not upload all the 3.7.0 files when you upgraded. Please reupload all the 3.7.0 non-image files. Then run install/finalupgrade.php. Make sure that you see versions 3.7.0 in the upper right hand corner of the page.
If you still have this problem after that, then try this. Create a new style and choose no parent style. This will force it to use the default templates. Then change to this style and view your forums with it. Do you have the same problem? If not, then this is a problem with your custom templates. You will need to revert your templates and redo your changes.
If you do, empty your browser cache, close all browser windows and try again.
If this is still not resolved, then reupload all the original vB non-image files (except install.php). Make sure you upload these in ASCII format and overwrite the ones on the server. Also be sure to upload the admincp files to whichever directory you have set in your config.php file. Then run 'Suspect File Versions' in Diagnostics to make sure you have all the original files for your version and that none show 'File does not contain expected contents':
Admin CP -> Maintenance -> Diagnostics -> Suspect File Versions
[Note: In some cases you may also need to remove any of the listed .xml files in the includes/xml directory.]
Next, disable all plugins, except the official Blog and Project Tools ones from vB. Also make sure that you are running the latest version for those add-ons if you have them. Now empty your browser cache and try again.
NOTE: If you had any add-ons installed, these will may need to be updated for 3.7.0. You will need to contact the authors of your add-ons about this. See post #2.