sql server 2008 version upgrade failed access to path is denied

upgrading from 2008 r2 eval to 2008 r2 enterprise.

Use the maintenance option from setup. Get pretty far along in the process.  But then the following error. ( an additional note. setup warns that I am running sql server on a domain controller server. )

The link the error message points to has nothing to say. Why would my sql server upgrade fail? If I have to reinstall, will I lose my database data?

thanks,

TITLE: Microsoft SQL Server 2008 R2 Setup
------------------------------

The following error has occurred:

Access to the path 'C:\Program Files\Microsoft SQL Server\100\License Terms\SQLServer2008R2_License_ENT_1033.rtf' is denied.

Click 'Retry' to retry the failed action, or click 'Cancel' to cancel this action and continue setup.

For help, click: http://go.microsoft.com/fwlink?LinkID=20476&ProdName=Microsoft+SQL+Server&EvtSrc=setup.rll&EvtID=50000&ProdVer=10.50.1600.1&EvtType=0x60797DC7%25400xBB814387