Our by-laws state that only men may be members of the Board of Directors. Our Board of directors are also the adminstration of the Islamic Center. What can we use as a daleel for preventing women from being members of the Board of Directors? What is your advice to the women who want to be members of the Masjid admininstration and participate in the decision making process?

All praise be to Allah, and may his peace and blessings be on the last and best prophet and messenger, Muhammad.

There is no evidence to bar the women from the board of directors in a masjid. This is not the general authority (welayah ‘ammah) that is not supposed to be given to women.
Most of the time however, the reason of not having them as members of the board is logistic, since the board may meet at times inconvenient for Muslim women, or even in places that are not appropriate for them to go to alone, such as the homes of some of the members who may also be single..etc.
I think, if the reason behind not having them on the board is logistics, the best solution to avoid inconveniencing them, yet allow their participation is to have a separate board for them that will decide the matters that pertain to them and their quarters and will be consulted regarding the matters that pertain to the whole center.

Allah knows best.