Attribute / skill can't be raised any further.
No error.
Tried to spend more experience than you have available.
Must be logged in
You are not trained in this skill
Tried to perform an action that is only valid on your character, on another character
Server complained. See ActionResult.ErrorString for the reason.
Request to the server timed out.
Spending this much experience would "overflow" the attribute / skill. You need to cap spendExperience at the total amount left to max the attribute.