(1Cor 15:51-52) “51 Behold, I tell you a mystery. We will not all sleep, but we will all be changed, 52 in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we will be changed.”
From this verse it looks like that Paul claims that he will not be among dead when “we will be changed” events happen. We know that it is not true.
But claiming “we will be changed” does not imply “we will be not dead”. It can be understood as “we, both alive and dead, will be changed”.
So there is no error here.
The God’s word expressed through Paul is errorless, despite of that Paul seemingly meant something erroneous.