SendKeys has special syntax for CTRL/ALT/Shift keys, so you need to send the key with shift pressed as well.
"+(,)" would be Shift + ,
"^(,)" would be CTRL + ,
"%(,)" would be ALT + ,
You may need to use < instead of , not sure though. Didn't test, this is just from looking at the MSDN page, it says all this info on it.