Dreamweaver will not allow me to select Undo from the Edit menu. It seems to be disabled as well as the Redo command. I cannot figure out what I have done! Please help.

You can check to see what your "Maximum number of history steps" is set to in
the General category of Preferences, but "2" is the minimum possible with CS3.

When you try to undo or redo, make sure you have the correct file selected in
DW. For instance, you can't undo a change made to index.html if style.css is
selected. That would simply undo the last change made to the style sheet if
"undo" is available. It won't be available if no changes have been made to the
file in the currently selected tab.