Actually the set control value method works fine...I just discovered - that is if the front panel of the called VI is included. The first time I encountered this problem using "set control value" I contacted NI but they never pointed out that, so I found a workaround and have not tried it since, however now I saw the following post and tested it. So that's probably not your problem, but anyway...:
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000AB4F0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0&USEARCHCONTEXT_QUESTION_0=set+control+value+does+not+work&USEARCHCONTEXT_QUESTION_S=0