i have checked your backend. It seems that you can not upload files in your jDownloads categories folders. Please check the folder access rights with a FTP programm CHMOD settings and OWNER).
In a second try, i have used the files manager from jD to upload files. But also here is this not always possible.
At latest i would check the system informations from your Joomla installation. But as result i get only this MySQL Error:
An error has occurred.
1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'TABLE 380' at line 1 SQL=SHOW FULL COLUMNS FROM TABLE 380
See pic. It seems that your Joomla installation is not full correct.
Your problems are not any jDownloads bugs...