You'll need to do some checking. (Note: if you had indicate what happens exaclty when you try to edit one of these fields, the following list would be shorter.)
Enter layout mode and click a field that does not allow you to edit it. Go to the inspector while it is still selected and check what checkboxes are selected in the Behavior section of the Data tab. If "browse mode" access is not enabled, select that option and you will likely be able to edit data in that field.
If not, double click the field to see if button setup or specifiy field opens up. If you get button setup, the field is set up as a button and you have a choice--ungroup the field to destroy it's button setup, or don't use this layout to edit that field.
If not, right click (option click) the field and select the script triggers menu item. If there's a scirpt trigger specified, open up that script and see if there is any code in the script that might be preventing you from editing data in the field.
If that's not it. Note the name of the field and go to manate | Database | fields. Make sure that this is not a field of type calculation. Caldulation fields cannot be edited. If it's not a calculaiton, double click it to open Field Options. check to make sure that the "do not modify" option has been specified.
Thank you! That helped a lot. It was the first option.