Crashing when going to a network

I am running AE CS6 on a MacPro 10.7.5 with 12GB ram and have done all of the adobe updates. When rendering out in H264, if I resize my project to NTSC SD from HD, limiting the bit rate to 1000kb therfore making the file under 1GB I can render out to my network drive with no issues. However, if I render out anything H264,(or Animation with best Settings, or ProRes HQ ) with no limits or resizing larger than 1GB to my network AE starts to lag and then eventually will freeze.