Network Movies- Some play some don't

[mrgilkes]

I have an iMac with all of my movies stored in the office upstairs and have a MBP floating around the house. I can easily access and play the movies on the iMac at the iMac, but when I try and link the MBP to the iMac in network folder only some of the movies will play. All of them will load and be seen over the wireless network, but like I said, some will play and others will not. Any help would be great.
Thanks