Whenever I try to upload an image by clicking the "Browse Server" button I get this...

Which typesetter - version do You use ? Do You use a javascript-blocker ? That would disable many functions in ckeditor .

Can You try "uploaded files" in the Adminconsole  - this loads the files to /data/_uploaded. 

* If You load pictures with ckeditor, just click at the site -> ckeditor -> image symbol - > browse server etc.

The above picture looks otherwise like  like a bad installation. Evtl. You can remove the error with  "tools/uninstall prep -> restore" which resets the rights.

I prefer ftp -  installation with filezilla portable. Other users had problems with other ftp-clients before ! (it may already help to overwrite the /include - directory with filezilla)

After transfer just klick at the installation-directory and right mousekey : 755 - also for subordinate directories and files - and then  install from the browser.

Using version 5.1. I am using Ad Block, but I disabled it for my site. I tried other browsers as well (Edge and Firefox) but got the same result.

 

Just did a fresh install of Typesetter 5.1 by transferring the files to my servers root directory and am getting the same issue.

The problem is  unclear. Have You saved (and published)  the site before You tried to upload the picture ? It looks like an error in the code of the site. Can You try to upload a picture in an empty new site ?

Do You have the same error if You go to "content >  upload files " ? Do You use a WebControl panel like Plesk ?

( Evtl. You should better  the CMS  install into a subdirectory of the root because of filters of the provider. Can You try another installation with with filezilla --- and use the CE-Version or the github master  (most advanced) instead of  the 5.1 which is not really php7.3+-ready. )

 

Is it possible that some file size limitation has been exceeded?