Thanks for the fast answer,I think that I get the answer by miself:
I was using local variable named "o".
o=createobject("class1.cls")
s=o.method1(param)
if I use another variable named loCls it works.
loCls=createobject("class1.cls")
lsStr=loCls.method1(param)

Is there any problem with variable name?
Sure yes...
Thanks,
Ibai