Problems with new installation

I’m new to Piwik and to this forum.
I just installed Piwik on my Ubuntu VPS server and am having problems getting it to work. Generally the install went well but now that I go to use it I get this error message:
Oops… there was a problem during the request. Maybe the server had a temporary issue, or maybe you requested a report with too much data. Please try again. If this error occurs repeatedly please contact your Piwik administrator for assistance.
I do not know how to begin debugging this. My server is working fine. One other thing that I do notice is that my Apache error log for this install directory has messages saying “client denied by server configuration:” but I wouldn’t know how to interpret that. I went through the related page at:
I get ‘Oops... there was a problem during the request.’ or ‘Internal Server Error’ or ‘500 error’ or the ‘White screen of death’. How do I proceed? - Analytics Platform - Piwik
…but it didn’t help.
The website is a wordpress site. The WP-Piwik plugin is installed and - as best as I can see - it is installed and working correctly. There was an error message but I fixed that issue.
I am very familiar with Linux and with the command line. Can anyone point me in the right direction. Thanks.