Is using the term "aforementioned" sometimes considered bad practice?

Solution 1:

No, aforementioned is formal and permissible in all scenarios where it is grammatically correct.

An example:

Indeed, scientific metaphors and analogies surface regularly in the text which, as noted earlier, is easy to follow with persistence on the part of the reader but is strangely unrewarding. The main reason for this is that any sustained argument is notable by its absence, several of the chapters following Chapter 3 having the appearance of relatively self-contained papers. This effect is heightened by the aforementioned tendency on the part of the authors to detour into scientific or quasi-scientific concepts and analogies without really drawing out the significance of such discussion …

—Roy C. Wood, Service Industries Journal, October 1997

Unrelated, but in the picture you used there is another grammatical error "I hope to be able [to] use..."

Solution 2:

Bryan Garner, the expert on legal style says this:

Aforesaid; aforementioned: These LEGALISMS have little or no justification in modern writing. Garner, A Dictionary of Modern Legal Usage, p.37

So, if “aforementioned” is considered poor style in legal writing, what about in non-legal writing? Consider the following.

This morning I saw a dog. The aforementioned dog was a beagle.

Does “aforementioned” provide any greater precision? Is it any more precise than:

This morning I saw a dog. The dog was a beagle.

No, not at all.

Use of language such as “aforementioned” (or “said”) is simply a sort of putting on airs, a bit like trying to impress a common audience by wearing a tuxedo, top hat, and sporting a monocle. But for most audiences, this would just come off as silly. Likewise with faux-precise legalese.

Solution 3:

 I doubt anything is grammatically wrong with the word because it is an adjective being used in the place of an adjective. Also, despite its length, it's not an especially difficult word to understand. However, as a matter of idiom, the word My is the wrong determiner to be using. Here it would be more common to say "the aforementioned" instead of "my aforementioned" as using the word Aforementioned already implies that the speaker mentioned it, unless otherwise specified. I suppose this is less so because of the word's meaning, and more-so because the word is often used in monologues where there is no need to specify yourself. It may even be preferable to say "the aforementioned" in these cases, since it gives a higher impression of impartiality.
 As a matter of fact "the aforementioned" is usually preceded by the word "The", and perhaps often enough that the grammar checker ignores the potential validity of any other determiner. Searching the British National Corpus reveals that 97 out of 114 results are for "the aforementioned". Google Ngrams* suggests that at least half of the written usages of "aforementioned" are for "the aforementioned" in any given time period after 1604. In more recent times, that gap has closed somewhat but the difference in usage remains roughly correlative with more recent trends of increasing popularity and they are beginning to diverge. There is some usage of our and my aforementioned, but they do not register on the chart.
 I am almost willing to bet if you replace "my aforementioned" with the aforementioned, that Microsoft Word will be willing to forgive your use of the word. I do not have Microsoft Word, but I entered the sentence in question into GrammarCheck and received a mark on "aforementioned" with the original, but passed the check after I made the suggested substitution.

 Now some people might take this to mean that you must use the definitive article, but I did see a few other grammatical determiners used on the British National Corpus and would be just as willing to use most of those as well despite the fact that it is a less common practice. This is especially so since nobody else here mentioned this oddity before I posted this answer.

*_{Here's a screenshot backup of the chart at postimg}