Getting Error: Out of memory during test execution

Problem detail:   When we ran a test for 100 users with Local host as LG and application under tested was .net web application, after 50 users are ramped up, we got
Action.c(112): Error -26000: Error: Out of memory !, Snapshot Info [MSH 4 9]
and all the users went to failed status.
But when we saw the event manager logs in the controller machine, there were no errors at the time of test execution.

The script used has viewstate and eventvalidation correlations.

Request you to look into the issue as why we got this error.
Please find below details:

We are using WinServer 2008 Enterprise SP2, Ram 72gb, CPU X5650 2.67ghz.
Logged in as local administrator
the box was used as localhost

Problem Solution:  No solution given