Posted By hbilbrey on 13 Apr 2021 10:28 AM

This particular issue began immediately after installing a module on a page that was supposed to already have it (and did on an alias) and then refreshing the page when it didn't display.

To me what you wrote is confusing. Did you install a module (upload an install package) or place an alread installed module on a page?
Also; what module was this?
 

Posted By Timo Breumelhof on 15 Apr 2021 08:11 AM

Do you mean you have 2 DNN installations using the same database (might lead to a lot of issues)? Or 2 DNN portals within the same DNN installation (normal user case)?

 

One production database, two DNN installations both using it. The second installation was a copy of the first, so they look nearly identical - which is why we didn't catch it for a while until cracks started to show.

As for your module question: 

On one of these installs, the module appeared on a page (we'll call this Site 1). On another, it did not (Site 2). I installed the module to Site 2, then placed it, hoping to have it appear on the page. It didn't; so I tried to place it again. I checked the page in the admin toolbar and it showed three instances of the module, so I removed two.

Still nothing. I cleared my browser cache thinking on an off chance it could be related, and that's when I was treated to the site going down to the internal server error. Stranger still is the copy, Site 1, continues to run just fine on the DB and now displays an extra copy of the above module on its page.

The module is a custom one used to display some data in a chart. It's one of many we've used over the past four years.

Posted By Sebastian Leupold on 13 Apr 2021 08:03 PM
there are a number of tables being written upon module install (ModuleDefinitions, DesktopModules, PortalDesktopmodules and others) and other tables, when a module is placed on a page (Modules, TabModules, ModuleSettings, TabModuleSettings, ModulePermissions and module specific tables as well).
System.InvalidOperationException: Sequence contains more than one matching element indicates, the error is happening in advanced URL rewriter, which tries to resolve page to load for an URL. this uses TabURLs, tabs and PortalAlias table.

Appreciated - I will check those tables to see if I can find duplicate rows. There have been some admin log errors for a while about the system selecting one resolution over another for some pages, but nothing as much of a hard stop as this error.

Check your WebServers table in dnn db for extra rows seems to cause resources confusion