Hi , Thanks Esteban, I have install pharo 5 and another issue appear when working with it. when i create a class and i try to inspect the class am having the following issue: Here is my class: Object subclass: #InterfaceDev instanceVariableNames: 'errbuf' classVariableNames: '' package: 'Network-sniffer when I inspect it i have: Object subclass: #InterfaceDev instanceVariableNames: 'errbuf' classVariableNames: '' Variable or expression expected ->package: 'Network-sniffer' With this i cannot initialize my instant variable "errbuf" Best Regards A. Tsombeng -- View this message in context: http://forum.world.st/Using-FFI-MessagetNotUnderstood-InterfaceDev-class-ffi... Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.