Update to provide Event Log entry:

AssemblyVersion: -1
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL:
AbsoluteURL:
AbsoluteURLReferrer:
UserAgent:
DefaultDataProvider:
ExceptionGUID:
InnerException: Value cannot be null. Parameter name: type
FileName:
FileLineNumber: -1
FileColumnNumber: -1
Method:
StackTrace:
Message: System.ArgumentNullException: Value cannot be null. Parameter name: type at System.Activator.CreateInstance(Type type, Boolean nonPublic) at DotNetNuke.Framework.Reflection.CreateObject(String TypeName, String CacheKey) at DotNetNuke.Services.Search.ModuleIndexer.GetModuleList(Int32 PortalID)
Source:
Server Name: MYSERVER

This took some extensive clicking to reach, because while links on most pages work, most admin links do not.

pfunk:  Do you have any events just before or after that one that shows the inner exception(s)?  That would show us the provider that is having the problem.  If not, temporarily set the "CustomErrors" to "Off".  Then view the site, and you should be shown the inner exception(s).

Of course, I spoke too soon. 

After making 3 successful edits in a row and then browsing to another page, I am now unable to even get to the editor window by clicking "Edit Text" link.  I can get to it by pulling down the menu from the triangle icon and choosing "Edit Text" for the module I wish to edit.  Clicking the "Edit Text" link simply reloads the same page in View mode (Design icon shows a minus).  The same happens when I click the "Update" link on the text editor window.

My Event Viewer is not showing any new items since the time around my last successful edit, but it should be noted that I can't even get that to change the number of events shown.  It seems even the controls for the Event Viewer page are failing somehow, thus preventing me from seeing new errors.

In my Event Viewer there seem to be two alternating General Exceptions over and over.  They are:

1)

AssemblyVersion: -1
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL:
AbsoluteURL:
AbsoluteURLReferrer:
UserAgent:
DefaultDataProvider:
ExceptionGUID:
InnerException: Could not load type ''.
FileName:
FileLineNumber: -1
FileColumnNumber: -1
Method:
StackTrace:
Message: System.Web.HttpException: Could not load type ''. ---> System.ArgumentException: String cannot have zero length. at System.Reflection.Assembly.GetType(String name, Boolean throwOnError, Boolean ignoreCase) at System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) --- End of inner exception stack trace --- at System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) at DotNetNuke.Framework.Reflection.CreateType(String TypeName, String CacheKey, Boolean UseCache, Boolean IgnoreErrors)
Source:
Server Name: MYSERVER

2)

AssemblyVersion: -1
PortalID: -1
PortalName:
UserID: -1
UserName:
ActiveTabID: -1
ActiveTabName:
RawURL:
AbsoluteURL:
AbsoluteURLReferrer:
UserAgent:
DefaultDataProvider:
ExceptionGUID:
InnerException: Value cannot be null. Parameter name: type
FileName:
FileLineNumber: -1
FileColumnNumber: -1
Method:
StackTrace:
Message: System.ArgumentNullException: Value cannot be null. Parameter name: type at System.Activator.CreateInstance(Type type, Boolean nonPublic) at DotNetNuke.Framework.Reflection.CreateObject(String TypeName, String CacheKey) at DotNetNuke.Services.Search.ModuleIndexer.GetModuleList(Int32 PortalID)
Source:
Server Name: MYSERVER