I'm running on version 1.5.4

Getting: WARNING: An Error occurred, please refresh the page and try again.

I'm having problems with the /logs folder not being written to since 2014, I'm getting an error message on an INSERT statement to the database from a .php file despite writing it as many different ways that I can find in other zen cart .php files. The error I'm getting is WARNING: An Error occurred, please refresh the page and try again. (I have looked at all the forum posts with this error message and it says to look at the /logs file) I also have a /cache file (not sure why, because I'm on 1.5.4), but that's not being written to today either.
The permissions on the /logs file was 755 (which is probably OK?) but I tried changing the permissions to 777 and I'm still not getting a file being written to in that folder today either . I've tried going to admin/tools/store_manager and purging the /logs folder and I get an HTTP 500 error message when I try and do that!

Has anyone got any idea as to why the /logs myDebug file isn't being created/written to please?

Thanks