Site: http://www.eco-mentor.com
Built in December 2012 with WordPress 3.5.1, theme inFocus 3.0 from mysitemyway.com, and a variety of plugins, including your dashboard, Affiliates, and MarketPress. Everything was working fine, but because of security issues, it was thought it would be best to bring things up to current revs. WP, plugins and your Dashboard updated fine, but when MarketPress (old version) was activated, it would cause the error:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
In this state, although the web site was “up” and browse-able, the entire dashboard area was unusable and would only display the above error screen. In order to regain control, I had to go into the database and reset active_plugins to a null value. I figured I just needed a current version of MarketPress, so I paid $19 and got the new version. It didn’t help — same results. A bit more testing revealed that your dashboard and MarketPress would operate fine without any other plugins activated, but at some point in activating other plugins, the above error would occur again. I haven’t been able to determine any one plugin disagreeing with MarketPress, because I can enable each individually in combination with your dashboard and MarketPress without any problems happening. It seems to be come combination of plugins, but I haven’t run all permutations to determine the exact combination which causes failure. We are not concerned with the Affiliates plugin, as sales have been very low and it wasn’t doing anything for us or our affiliates. We DO, however, need MarketPress to function, as without it our store page [https://www.eco-mentor.com/store12/#learning-tools] is rather useless.
The plugins (besides the 3 of yours I mentioned) we are using, and were using successfully prior to the upgrade are:
Groups v. 1.4.10
Jetpack v. 3.1.1
Mailchimp v. 1.4.1
Mailchimp Widget v. 0.8.12
Sidebar Login v. 2.7.1
Simple Access Control v. 1.4
WordPress HTTPS v. 3.3.6
WordPress Importer v. 0.6.1
WP Popup Plugin v. 0.5
[Versions listed above are the current updated versions. I don’t know what versions were being run on the old 3.5.1 WP.]
Another test I did was to see if it was simply a matter of quantity of activated plugins, and that’s not the case either, as I was able to activate some other plugins which would normally be disabled and got up to more than 12 acitve plugins with no problems (of course MarketPress wasn’t one of the active ones.)