What exactly is a “morphological error”?

Please look at the following sentence:

“When did the test began?”

I feel that the use of the form “began” instead of the correct form “begin” is a classic example of a morphological error. However, I am having some difficulty understanding it clearly. If this is an example of a “morphological error”, can anyone give a clear and concise explanation of why it is so? Also, can anyone give a straightforward explanation of what a morphological error is in general? Any postings are greatly appreciated.

In the field of language, morphology means the structure of words, how words are formed, and how the parts fit together. If you get the wrong morpheme (i.e., word part) in the wrong place at the wrong time, you’ve committed a morphological error.

Morphological errors would be things like:

“He putted the plate on the table.” (A past tense morpheme has been added to the verb, but it’s not supposed to be there.)
“They have six childrens.” (The word “children” is already plural, but someone has added a needless plural suffix.)

There are also phonological errors, where people get their sounds wrong. When a professor wanted to say, “You have wasted the whole term!” he made a mistake, switched two sounds around, and said, “You have tasted the whole worm!” That’s a phonological error. A girl from Thailand once wanted to tell me, “Then I got on my bus and rode back to the capital,” but she made a phonological error and said, “Then I got on my butt and rode back to the capital.” That’s another phonological error.

Then there are morphological errors that are caused by phonological errors. I heard a girl who sometimes removed the T from the end of the word “breakfast” say “breakfases” instead of “breakfasts”. Removing the T made her put the wrong form of the plural suffix on the word. That was a phonological error that resulted in a morphological error.