The file is last time present in OJS 2.4.8, thus I recommend to check your OJS code for consistency. It seems that it doesn’t correspond to the version you specified.
I suggest solving this issue step by step. First I would check why there is a call to a non-existing file. Other errors can be evaluated when this problem is resolved but if you have concerns, you can post relevant errors here.
Indicate that we have version 3.1.1.0 … it could be that error due to migration. We did it over a year ago and it gives us no problems. I look forward to how to proceed.
The file was in the ftp folder. The overwritten to which you have instructed me to download.
Does this error message contain any info regarding from where the call to JSONManager.inc.php is performed?
The last part isn’t specific, according to it, it’s just an import statement that is called somewhere.
As it appears to happen when accessing the plugins page, it should be from one of the plugins. Thus, if any additional info is absent, check if there aren’t any outdated plugins that come from OJS 2.4.8.
What are paperbuzzviz and portico folders? I’m not familiar with those.
Once again, check if all the content of the plugins folder corresponds to the release. I usually use diff tools to compare the code.