Thanks Vlad. That was the problem.

Mark

>Is your second form Modal? It must be modal.
>
>Vlad
>
>>>I have a form with a private DS which includes a command button whose click method is as follows:

>>>nSessionId=ThisForm.DataSessionID
>>>oForm=createobject("AddMilestone")
>>>set datasession to oForm.DataSessionId
>>>use Milepick order milestone
>>>set filter to Milepick.MileId<>999
>>>*oForm.lstMilestones.RowSource="Milepick.milestone"
>>>oForm.lstMilestones.FirstElement=1
>>>oForm.lstMilestones.RowSourceType=6
>>>oForm.lstMilestones.Value=1
>>>oForm.Show()
>>>oForm.Activate()
>>>*read events
>>>nId=oForm.nMileId
>>>use in Milepick
>>>oForm.Release()
>>>set datasession to nSessionID
>>>if nId=0
>>>   =Messagebox("Milestone addition cancelled.",16,"Notice...")
>>>   return 0
>>>endif
>>>dimension AddMile(1,5)
>>>AddMile(1,1)=R6Snc.PWS_ID
>>>AddMile(1,2)=R6Enf1.EnfId
>>>AddMile(1,3)=nId
>>>AddMile(1,4)=R6Enf1.Act_Type
>>>AddMile(1,5)=R6Enf1.Docket_1
>>>Insert into R6Mile from array AddMile
>>>=TableUpdate(.t.,.t.,"R6Mile")
>>>ThisForm.Refresh()

>>>I have tried it with and without the "READ EVENTS", trying to set the RowSource in the listbox causes a "Syntax Error" but commenting it out still allows the RowSource to come from the field I want.
>>>
>>>So what's the problem, you ask? One, the code never switches control to the new form (with and without a READ EVENTS, oForm.ACTIVATE(), etc.). I already have 1 READ EVENTS in effect after DO MYMENU.MPR in my startup .PRG. Then when I release the form, I try to go back to the previous forms private DS, and the line "SET DATASESSION TO nSessionID" gives me an "ILLEGAL OPERATION" message, then blows me out of VFP.
>>>
>>>I have done this very same thing by pasting the above code in its own .PRG and it works fine. The form I am instantiating is in a class library I developed for this application.
>>>Help? TIA.
>>
>>Done in code except for trying to switch between Datassessions, of course.