Hello I would not think this is a vbulletin issue as you have an upload link which means your
vb file is doing its job
If anything maybe new templates where not uploaded this would explain it. Also if your server file uploads are turned off it would explain it so two things to try
Make sure to upload all 5.21 files except the config files incase any where missed
Next if the issue is still there link me a phpinfo file to see