What did he command?
Rashi: Announce to cease Bnei Yisrael from building the Bayis and the city, until I will command to build the city.
What is "Ilach"?
Ibn Ezra: It is a little like Alein (these, i.e. people).
How could Koresh cease building? He wrote that Hashem commanded him to build the Beis ha'Mikdash! And what is written in the name of the king and stamped with his ring cannot be retracted in the statutes of Paras and Madai (Daniel Perek 6, Esther 8:8)!
Malbim (7, 23): The king's written command cannot be retracted even if it was based on a mistake, like I explained in Esther! There were two ways to understand the king's command. (a) They should stop building the Mikdash. Surely he did not mean to stop building the city, for they had not started. However, he additionally commanded not to build the city until he authorizes this. However, the king received a letter saying they were building the city, and not the Bayis! (b) Surely he meant to stop building the city. His Heter to build the Bayis was still in force. It could not be retracted! Rechum and Shimshi translated the king's letter. They said that the complaint was about building the Bayis, and this is what the king commanded to stop.
