Response: Having a wet dream whilst in the state of ihraam for the Hajj or the ‘Umrah does not affect the Hajj nor the ‘Umrah, so they are not invalidated. Whoever experiences this should make the ghusl for the janaabah after waking up from the sleep, if he saw semen, and there is no expiation upon him because having the wet dream was not out of choice.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu `alayhe wa sallam) and his family and his companions.
The Permanent Committee for Islaamic Research and Fataawa
Fataawa al-Hajj wal-‘Umrah waz-Ziyaarah – Page 64.fatwaonline.com