The "Fake Ex Muslims" (FxM) site has a page of "issues" that are identified with respect to Ergun Caner (link to page).
I'd like to respond to a few of these "issues."
1) Injeel means Angel?
In one video that FxM has identified, Ergun Caner stumbles over the Arabic word for an evil spirit. The Arabic-root word he was looking for (and initially says) is Djinn (from Arabic جني jinnī). Then, however, Caner makes a terrible blunder and follows Djinn with "Injeel" which is an Arabic word for the Gospel.
Result: Embarrassing slip of the tongue that suggests that Caner's Arabic is not fluent.
2) Prophet Bahruch
In one video that FxM has identified, Ergun Caner lists something that sounds like "Bahruch" as one of the prophets of Islam. It may be that Caner is referring to the Old Testament dubious military hero Barak, who famously was afraid to go to battle without Deborah by his side. This is still a bit strange, because Barak is not really referred to in the Old Testament as a prophet, although Islam tends to claim the Old Testament prophets as being among her prophets.
Result: Puzzling comment from Caner.
3) 40 Days of Ramadan
In one video that FxM has identified, Ergun Caner slips up and says that there are 40 days in the lunar month of Ramadan. This is, of course, simply a conflation in Caner's mind between the 40 days of Lent in Romanism (and Eastern Orthodoxy) and the shorter 29-30 day months that are lunar months.
Result: Embarrassing conflation between Romanist and Muslim fasting practices.
4) Ergun's Shahada
In one video that FxM has identified, Ergun Caner slips up in two ways. First, he recites the wrong Arabic text when trying to state the Shahada (he quotes instead the opening lines of the Koran). Second, when he gives the translation of the Shahada in English he adds "final" or "greatest" into the translation, although there is no literal basis for that expression in the Arabic.
Result: Embarrassing pair of mistakes that strongly suggest that Caner is not very familiar with Arabic.
5) Jesus is the Messiah
In one video that FxM has identified, Ergun Caner suggests that Muslims believe that Jesus was only a messenger and not the Messiah. However, of course, Muslims also call Jesus the Messiah. It's unclear from the clip whether Caner is aware or unaware of the Muslim claims. Christians recognize that being the Messiah involves being the Son of God. Muslims reject the idea that there is such a thing as the Son of God. Thus, even if they us the term "Messiah," they mean something different by it than what we mean.
Result: Ambiguous alleged error.
6) Shabir Ally Dead?
In one video that FxM has identified, Ergun Caner refers to someone he calls "Shabir Ally" and states that this man was a leader, a debater, and is now dead. That's troubling, because Shabir Ally (one of Islam's leading debaters in North America) is very much alive. What Caner almost certainly meant to refer to is the late Ahmed Deedat. However, Caner used the wrong name.
Result: Embarrassing transposition of names, confusing that of one famous Muslim debater for that of another famous Muslim debater.
I haven't addressed all of the alleged errors attributed to Ergun Caner, but I've addressed some of the big ones. Others include some of the details surrounding Caner's conversion (the exact dates and relative dates between Caner's conversion and the conversion of his two brothers). Also, the birthplace issue that I've already mentioned in a previous post is brought up.
What is the conclusion of all this, though? The impression that I get is that Caner doesn't seem to remember that much Arabic from 25 years ago, assuming he ever understood Arabic at that time. It also appears that Caner has a tendency to get some of the details mixed up during his oral presentations. However, nevertheless, it does not seem to be reasonable to suggest that Ergun Caner is faking the whole fact that he was a Muslim as a child.
Ergun Caner has himself responded to these (at least I think it is these, or at least some similar charges) and his response can be found at the following link (link). His comments there are unequivocal and maintain his claim to having been a Muslim. However, as noted in a number of the videos, he was converted as a teenager in 1982. So, it has been over 27 years (at this time) since he was Muslim. Does that make some of his mistakes (identified above) less embarrassing? Only a little.