The 'Load a File' button is grayed out when opening a BLOB column in the Schema Browser.
Data in the columns are set to 'Read Only'.
In the Data tab of the Schema Browser, un-check the 'Read Only' check box (close to the commit and rollback buttons), then the button will be enabled.
If the 'Read Only' check box is un-checked in the Data tab of the Schema Browser and the Load button is still grayed out. Go to:
Toad Menu | View | Toad Options | Data Grids | Data and un-check "Use read-only queries".