The memory of most of our PLC5 processors was wiped and we found that it was related to the revision level of the processors. The blame was pointed at an Ethernet storm that the earlier rev. processors could not handle and wiped their memory. The Ethernet storm caused by a third party software package sending ethernet broadcast frames. We had our affected processors upgraded to Series E rev E.2 or Series D rev F.2 as well as upgrading the ethernet sidecars and no trouble since.