After some updates of Wordpres and Wpforo the maximum file size in posts get limited to 50 Byte. Before it was 50 Mega Byte and worked fine.
Here some screenshoots of my settings and this issue:
Server settings and wpforo settings all looke fine. Maximum file size is there 50 Mege Byte. So I don't know, what could be wrong here?
Thanks for your help!