ActiveX - Synchronization error

Hi,
I am relatively new to QTP. I was trying to use QTP on a VB/ActiveX application and when i run the script, i get the following error :-

"Automation Error - An outgoing call cannot be made since the application is dispatching an input-synchronous call"

my code :
VbWindow("mdiMONETEMR").ActiveX("SSListBar").Click 40,218
VbWindow("mdiMONETEMR").VbWindow("frmProblems").VbEdit("txtCommonName").Set "a"
VbWindow("mdiMONETEMR").VbWindow("frmProblems").ActiveX("ActiveX").AcxTable("True OLE DBGrid 6 Control").ActivateCell 1,3
VbWindow("mdiMONETEMR").VbWindow("frmProblems").VbComboBox("cmbProblemCertainty").Select "Definite"
VbWindow("mdiMONETEMR").VbWindow("frmProblems").VbButton("ThunderRT6CommandButton").Click

The bold line above is where the error is

basically , its a text control with a grid just below it(just like a dropdown). When i type 'a' in the textbox, it lists all values starting with 'a'. When we select an item , it puts the text back on the first textbox.

Thanks for your time,
majesh