Invalid recipe - make sure you have all of the required components and nothing extra is in the workbench
Insufficient caster level - self explanatory - note that this may be bugged in certain game versions
Do not have (required) feat - self-explanatory
Not a base item - item may already be at 3 enchantment limit. Strangely this message can also be returned if you are using an incorrect recipe. Also double check to make sure you are using the proper workbench.
This section will be filled as more error messages are known to us.