Many thanks for the reply. I investigated the matter a bit further but have not got to a result except now I don't do the changes only download. I have done changes only download so many times on this system apart from other systems but never have had any problems. As far as SFC90 is concerned for this system we never have used sfc90 in the complete project not even been added to the project also the test function time is 90 minute.

Also if you look at the description of F_TESTC function it does say that it executes after every 24hr and it can be triggered by changes only download(but not defined what we should not do), don't know if there is any way to force it to execute just after download.I have the projectbackupbefore changes and I did the comparision using VXC(comparision attached). The interesting thing in the comparion is that the F_TESTC input parameter has been changed to 590 from 588andthat I think the cause for safety program shutdown but I can't explain why it happened during the compilation because you can see the changes Imadeare not something special.

Now I am really looking for the thin moral line(becausecfc editor don't bother to give a message) where its illegal todo changes only download. I cannot take a riskto do changes only download to any of the F-system until I can find the exact boundary...I must say there is a grey area in F system.

Now once the system is shutdown then thesolution is that after fail-safe program shutdown set thesystem back to run and that’s it but I don't know how it can be prevented.

One more thing Siemens is also workingon this system. In their investigation first they said that it can becaused ifI have deleteda runtime group although they have not provided any supportive docsbut after looking at this VXC comparison now they do notseem very interested to find the grey area .