Thanks for your review, I think the problem is that you do not have enough RAM, the server only has 4 clients on it at the moment and is hardly being used.
Uptime / Load: 23:26:59 up 1 day, 20:23, 1 user, load average: 0.57, 0.49, 0.51
Correct the E-1500 has 2 users per disk, the E-750 has 4...