[objectName:channel]

This does not work in messiah:script.  Instead you must use a function called motchan( ) to retrieve those values.  The syntax is:

double motchan(object obj, int channelID, time t);

Return Value:
 

The value of the channel at the time 't'.

obj: object to retrieve channel info from

channelID: identifier of the channel to retrieve info from, defines are provided for this value through messiah.h
t: time at which to retrieve the value (that is "the value of the channel if it were time 't' ")

Typically you'll use the defines from messiah.h for the value passed as channelID (e.g. xpos, XPOS, heading etc.).  But if you need to get the channel ID of a user defined channel, like channel 21, named "foo" on a slider, you could get it's ID by calling

int chanindex(object obj, string chanName);

Return Value:
The index of the channel chanName in object obj.