Comment #3 on issue 2792 by sebastia...@gmail.com: Process>>isTerminated raises an error time to time http://code.google.com/p/pharo/issues/detail?id=2792 I see a bug here too. I simply can't open the process viewer unless I use this pathed version of #isTerminated isTerminated self isActiveProcess ifTrue: [^ false]. ^suspendedContext isNil or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess. If so, and the pc is greater than the startpc, the bock has alrteady sent and returned from value and there is nothing more to do." (suspendedContext isBottomContext and:[ suspendedContext pc isNil]) or:[ (suspendedContext isBottomContext and:[ suspendedContext pc > suspendedContext startpc])]]