For what its worth I'm having the exact same scenario as Nick. DNN 4.4.1, Text/HTML module 4.05.00. 

I removed all *html*dll files from bin to a separate folder.  The site runs again and I can choose to add the module to a page but then get the message:  An error has occurred. Error: Text/HTML is currently unavailable.  I can change settings on the module but cannot add content due to the error.

How do I revert to a previous version of the module?  Thank you,

Mark B

I to have just upgraded 4.5.0 to 4.5.1 and I am getting the below compilation error. I do not have the dotnetnuke.modules.html.dataprovider.dll in my bin folder and I am at a loss as waht to do to fix this. My site is down and I need some help from someone please...

Orgbrat

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: BC30560: 'DataProvider' is ambiguous in the namespace 'DotNetNuke.Modules.HTML'.

Source Error:

Line 40: 
Line 41:         ' singleton reference to the instantiated object 
Line 42:         Private Shared objProvider As DataProvider = Nothing
Line 43: 
Line 44:         ' constructor