calling a tcl proc with arguments from another tcl proc

I have a tcl proc which takes arguments to replace a value on a field, I have another tcl proc which loop thru a repeating segment and calls the first tcl proc with argument. I get the following error

Tcl error:

msgId = message0

proc = ‘spuh_replace_fieldvaluein_repeatsegments’

args = ‘{SEGMENTNAME OBX} {FIELDNUMBER 3_1} {VALUETOBEREPLACE &} {REPLACEVALUE \T\}’

result = ‘can’t read “mode”: no such variable’

errorInfo: ‘

can’t read “mode”: no such variable

   while executing

“switch -exact — $mode {

       start {

           # Perform special init functions

           # N.B.: there may or may not be a MSGID key in args

…”