This may be cause by a bug in your program. LV does automatic memory management for you, and it's usually pretty good about it, but if you use functions that require more memory during run-time, LV will allocate more and more memory until you run out. Good examples of this are Build Array and Concatenate String. If you use these in a loop to build a large array and do it fast, you may run out of memory pretty quickly.
Try using the profiling tools in Tools>>Advanced (I don't think they exist in the base package) to see if you can pinpoint the consumption to one of your VIs. You should also read the white paper about memory management in LV. You can find it in Help>>Search the LabVIEW Bookshelf or by searching this site.
If this is consistent and you can't solve it, I suggest you post your code.
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