Process Monitor also shows a few ACCESS DENIED entries as I attempt to start the service. Here is one directly related to the agent:

Process Name: SQLAGENT.EXE

Operation: CreateFile

Path: D:\SQLData\data\MSSQL11.MSSQLSERVER\MSSQL\Binn\sqlsvc.dll

Result: ACCESS DENIED

Desired Access:Read Data/List Directory, http://www.sqlservercentral.com/Forums/Skins/Classic/Images/RichTextBoxTable/tbl_bottomleft.gifExecute/Traverse, Synchronize

Disposition:Open

Options:Synchronous IO Non-Alert, Non-Directory File

Attributes:n/a

ShareMode:Read, Delete

AllocationSize:n/a