I keep getting logged out of admin area on multi-network site

I run a multi-network site which currently hosts 2 multisites. I can log in and work in the admin area of the first multisite well without any problems. However, when I log in to my other multisite (using the same credentials) under the same multi-network, I am able to log in but keep getting logged out with every link I click. My session keeps timing out. How can I fix this problem?