Y'cant have the playmove in a INIT field

You need to put it in a script or a trigger
Heres whadda do :
Name the unit something (For eg guy01)
Put a trigger, activated by anyone
In the activation field, put guy01 switchmove "OnChair"
Make sure the trigger is over the guy (Or anyone.. Change the size to something huge, like 100000 by 100000, so it will deffintly get activated)
Hit okay etc, preview the mission

Hope you understand

- Ben
(BTW, inshort, just put the playmove thing in a trigger, with this replaced by the units name)