SIOD ERROR: not a number

Question

Some times when i use (SayText " ") it gives the following error: "SIOD ERROR: not a number". For example:

festival> (SayText "ਮੇਰਾ ਨਾਮ")      means (SayText"mera naam")
SIOD ERROR: not a number 
festival> (SayText " ਨਾਮ ")  
SIOD ERROR: not a number 
festival> (SayText "ਨਾਮ")

and when i backtraced it

SIOD ERROR: not a number 
festival> (set_backtrace t)
t
festival> (SayText "ਨਾਮ")  
SIOD ERROR: not a number 
BACKTRACE:
   0: (#<SUBR(5) Classic_Word> (quote #<Utterance 0xaddeb8b8>))
   1: (apply_method (quote Word_Method) utt)
   2: (Word utt)
   3: (let-internal
    (type)
    ((utt.type utt))
    ...)
   4: (utt.synth (eval (list (quote Utterance) (quote Text) text)))
   5: (SayText "ਨਾਮ")

not getting it can anybody tell the solution for this