The speaker tries to say that I could have explained what I mean more accurately which would increase the chances of him solving my problem. He says the following:
"Your attempt at explaining your problem was very inconvenient"
I checked the word "convenient" in the Longman Dictionary and none of the meanings it has make sense in this context. Is this an error?
"Inconvenient" is not merely unidiomatic when used in this way; it is incorrect. Convenience is an aspect of a physical goal or objective itself; it does not describe the method by which a goal or objective is achieved. Nor is it a descriptor of value, esthetic quality or craftsmanship. One would not describe a work of art, a blanket or a TV commercial as "convenient."
Most commonly, "convenient" is used to express the ease of reaching a goal. Examples: "The store is conveniently located." "The clinic is open at convenient hours." "The lockers are very high on the wall, making them inconvenient to use."
Statements like the one submitted are more useful if they provide specific suggestions. In this case, one might put it in the form of a question, i.e., "Could you share with me a step-by-step method of solving the problem?"
I would say yes, the semantics is off. The sentence would make sense in some other contexts, for example this one. While you were explaining your problem to the speaker, there were some other people present. Something you said in the course of your explanation caused these other people to become somewhat upset with the speaker; not very strongly or irreparably, but sufficiently so that the speaker will have to deal with it sooner rather than later—despite the fact that the speaker actually doesn't quite have either time or the energy for it. Dealing with it is therefore an inconvenience for the speaker, and so the statement makes sense.
Here are some better ways to put it:
Your explanation of your problem was [a bit confusing/confused/unclear/opaque/convoluted/overcomplicated]/[not as clear as it could have been]/[somewhat misleading]/[such that it initially led me down a wrong path].
It is not one of the usual terms that are used for speaking of the quality of a piece of writing. In other words, as used, it is not very idiomatic. To compound the incertitude there is the fact that you don't know whether the inconvenience was caused to the writer or to the reader, but in the end this might not matter.
The definition (not useful to you because it does not save you time or causes a problem), strictly applied, makes sense: for instance, if you use more words than are needed or explain things that are not relevant, then you are causing yourself an inconvenience since you make things more complicated than they have to be; as well this is an inconvenience for the reader. A usual term for this type of writing is "wordiness". However, you do not tell bluntly people that their writing is wordy, it is quite offending. You can do that when involved in an interaction concerning the skill of writing, as for instance in a teacher-student interaction. So, perhaps, your interlocutor is trying to be as polite as possible, and that leads him/her astray as far as using the proper terms. The problem could be other than wordiness, that was just the most typical example.
As linguistictum has explained, in other circumstances the given sentence could be considered to be acceptable, however, if one accepts infinitieunique’s interpretation of the intended meaning, “inconvenient” is incorrect.
The sentence could have been “Your attempt at explaining your problem was too [vague/imprecise/confusing] to [facilitate/allow] a proper [answer/resolution] of your problem.”
(Not relevant to the question but perhaps worthy of comment is that “Your attempt to explain …” would be preferable to “Your attempt at explaining …”)
Better still however would be to restructure the whole sentence to read: “Had your explanation of your problem been more [precise/detailed] it would have helped to produce a [better/more satisfactory] [response/answer] to your problem.”
