The most likely reason is that it has the "Deny log on locally" user right.
Run gpedit.msc
and go to Computer Configuration: Windows Settings: Security Settings: Local Policies: User Rights Assignment and find the "Deny log on locally" setting. By default this contains the Guest account; I think in your case you will find it also contains the ASPNET account.
You can add additional accounts to this list by double-clicking on "Deny log on locally" and selecting "Add User or Group".