Script Error

hello,
I want to use this script to grab the device configuration, but the configuration of the device can only split-screen display, so I want to appear when I'm waiting for the string to the next step, when the string does not appear, wait after a few seconds and then moves down.

I encountered a problem, when I run the following script:
sub main
xsh.screen.waitForStrings ("this",1000)
end sub


Always prompts me：“调用过程(sub)时不能使用括号。”

I do not know how to solve, please help me. Thank you!

Program Ver. : Xshell 4