I assume you are talking about 1 Corinthians 16:5 in which Paul tells the Corinthians that he is planning to come to them after visiting Macedonia. You say that he “promised” he would come, but that is not true. He simply shared with them what his plans were. We do not see the word promise there. Then you say (or perhaps a Muslim critic says) that in 2 Corinthians we learn that he never made it to Corinth, which implies that 1 Corinthians 16:5 is not inspired. First of all, we do not know for a fact that Paul did not go to Corinth as he said. The lack of specific mention of him going to Corinth does not prove that he never went there. We do not have a comprehensive list of all of the travels of Paul. In fact, if you go to 2 Corinthians 13:1 he tells the Corinthians that, if he comes to them, it will be the third time. This proves that he did indeed visit Corinth a second time, most likely after he wrote 1 Corinthians. I do not know who told you that this is an example of a biblical error. I would imagine that it was a Muslim who told you this. This person should do better research before they claim to have found a mistake in the Bible. I am afraid that this is typical of Muslims who try to prove the Bible is corrupt. They read the Bible, not to learn from it or to understand it, but to try to find “dirt.” This is a perfect example of their insincere approach, as they did not even bother to see if what they said was true. It was not, and Paul did visit Corinth after writing 1 Corinthians and before he wrote 2 Corinthians.
Besides, even if Paul had not visited Corinth a second time as he shared in 1 Corinthians 16:5 (although, apparently, he did!), Paul is simply sharing his plans. If he was not able to complete these plans, this would not make the passage uninspired. Paul was simply saying what he planned to do. If Paul had been prophesying, that would be different, but in the context he surely is not prophesying, but merely stating his intentions. This was not a prophecy which, if it were not fulfilled, one could argue it was a biblical error. It is simply Paul sharing his plan. Sometimes our plans do not turn out for one reason or another. This would not prove that God is not in control. It only demonstrates the insincerity of this Muslim critic.