The list cannot be displayed in Datasheet view for one or more of the following reasons:
A datasheet component compatible with Microsoft SharePoint Foundation is not installed.
Your web browser does not support ActiveX controls.
A component is not properly configured for 32-bit or 64-bit support
Doing some further research I came across this:
You cannot view a list in Datasheet view after you install the 64-bit version of Office 2010
The best part is: If your business needs do not require you to use the 64-bit version of Office 2010, we recommend that you uninstall the 64-bit version of Office 2010 and install the 32-bit version of Office 2010. A 32-bit version of the Datasheet component is installed with the 32-bit version of Office 2010.
There is a workaround which is to install 2007 Office System Driver: Data Connectivity Components
However, that has implications such as needing to uninstall and reinstall this should you need to add more components to Office 2010. That sounds like a disaster waiting to happen.