Difference between Changed,changed_Salesordere,Change_event

Hi All,

i am workin gon workflow where the scenario is like whenever sales order get changed it will display sales order and send a mail to user.

now the mail is workin gfine but in SBWP when i click on workflow. it is only giving me VA02 transaction and giving error that enter sales doc no.

how to solve this problem so that by clicking wf in inbox i can disply the so detail.

Thanks,

CHintan