"Zannennagara watashi wa 9 gatsu ni Paris ni iku jikan ga toremasen deshita" iku jikan ga toremasen deshita => this expression is so English grammared. Japanese native speaker would say "zannennagara watashi wa(ha) isogashikute 9 gatsu ni Pari ni ikenasou desu." ( Unfortunately, I will be too busy to go to Paris in September.) ikenasou = "probably not be able to go" *Japanese native people will accept this expression as he/she can't go, even it is saying "probably". For your question why its used past-tense, people usually don't use past-tense in this case of sentence; however, maybe the one who wrote this sentence was supposing that he/she was informed/realized that she/he will not be able to make it in September somehow BEFORE he/she write this sentence. That's why he/she used the past-tense in this case. This is my guess, but it's probably it.

It looks like he's saying: "He couldn't take the time." He was unable to take time (off work) to go to Paris next September. Now that makes sense, doesn't it?