Hi,
This is happening may be for few reasons.
-Plugin conflict
-Theme not supported in WP 3.8
-WordPress General Error
First of all deactivate all the plugins, then check the site & check for the issue. If it worked well, activate the plugins one by one & find which one is causing the issue.
Ask your theme author for checking if it supports WP 3.8 or not.
Try deactivating the theme & activating the default one & the re-activating your theme.
I hope these helps you, Thanks.
Hi Mrinal, it helped.
I did exactly what you’ve said. I deactivated all plugins and after activated them one by one. It worked, but it happens to be that none of the plugins caused the problems.
Thank you very much!