Mikeski47 wrote
I was able to view the /lib/exe/css.php file. [...] I did not see any error messages.
You have to look at the same time when the problem is appearing. If that is what you did, it might well be that there won't be any error messages. If there are any, I think they would contain the word "error" (but I'm not sure).
Do you have a URL you can share with us?
Mikeski47 wrote
Can you tell me where specifically I should be looking and what I am looking for.
That depends on your server and OS. Best google "error logs" together with the name of your server and your OS. (Apache's error logs can be under /var/log/apache2/error.log... or not, it can be configured differently.) If you cannot find it, better ask your hosting provider. It might also be that you don't have access to them, in which case you need to ask your hosting provider anyway.
Sorry, I cannot give you a more specific answer. It is not easy to know what might go wrong without the appropriate error message. It could be a full disk or wrong file permissions or a server misconfiguration or ... 20 other things...
It might not help, but you can try to add
?do=check to the end of your wiki's URL to see if there's a more general issue with your wiki. That will do some general wiki health checks and display some info messages.