JSON error in vb 5.4

[athamm]

Hello,

i get this error when i want to post in my board:
Error while saving the post: SyntaxError: Unexpected token G in JSON at position 5

I have vbulletin 5.4 version.
Servertype. Linux (Apache)

PHP: 5.6.34
Postsize 8,00 MB

MySQL-Version 10.0.32-MariaDB-0+deb8u1
MySQL-Paketsize: 16,00 MB

The Posts are saved but the message comes every time and the side load very slow.
Is there any idea how to fix it?