Here it says that the copper Mizbe'ach was in front of the Mishkan, which was in Yerushalayim. Was this not the Bamah in Giv'on (verse 3)?
Malbim (3): After Shlomo offered Olos in Giv'on, he took the copper Mizbe'ach and Klei Ohel Mo'ed from Giv'on to Yerushalayim. Verse 13 implies like this. Also Melachim I, 8:4 "va'Ya'alu Es Aron Hashem v'Es Ohel Mo'ed v'Es Kol Klei ha'Kodesh Asher ba'Ohel" implies that all of them were in Yerushalayim 1 , where the Aron was. From there he brought them up (to the Mikdash). If not, it should have said that he took them from Giv'on! If so, when did the take them from Giv'on? We must say that it was right after he offered the Olos; he realized that he transgressed offering on Bamos when the Ohel Mo'ed is in its place 2 . It was a toil to go to Giv'on each day, so he brought them to Yerushalayim. Then, (a) he offered in Yerushalayim on the copper Mizbe'ach, or (b) Bamos were permitted, after he took Klei ha'Ohel and the Mizbe'ach from Giv'on. This is why he gathered all the leaders, for the honor of the Ohel Mo'ed and its Kelim when he dissembled it.
