yes, that's likely to be contributing to your issue - sharepoint runs as the root website, and you seem to be installing dotnetnuke as a virtual i.e. DNNMedBill . Virtual directories inherit the settings and configuration of asp.net sites running in the root of the IIS instance.
If you're going to run DotNetNuke in a subdirectory, or run another asp.net site in a sub directory, to avoid this inheritance chain causing issues there are a number of steps to take

• Ensure that your subdirectory is an application in IIS.
• If the root level folder is running an asp.net site, then edit it's web.config and add the line below just before the <system.web> tag.
  
  

  <location path="." inheritInChildApplications="false">

  <system.web>

  
  
  

Clearing individual sections
Please note, setting the inheritInChildApplications attribute will ensure no inheritance on any items within system.web. This includes httphandlers, httpmodules,assemblies, authentication and other optional sections such as compilation and customErrors. If you need to ensure that a subdirectory obeys a setting from one of those (e.g. a common customErrors behaviour) you will either need to copy the relative section to the subdirectory web.config, or else you will need to remove the inherited settings at the individual levels using the <clear> directive e.g. to remove inherited httpHandlers in a subdirectory you would alter the web.config in the sub directory to look like:

Note: Care must be taken when doing this as it's possible to clear entries that are required for the running of the site. Typically you will add the <clear> entry to the first line of the relevant section(s) and retain the existing entry. This ensures that the entries are not duplicated.

Note: i usually find it easier to add a new IIS website and use that (adding host headers to point to your website)

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