I got it :)

this was the code I use to create my Form :

Scan for ordine > 0
	oform.addObject('_l'+Transform(recno()),'Mylabel')
	oCtrl = Evaluate("oform."+'_l'+Transform(Recno()))
	oCtrl = Evaluate("oform."+'_l'+Transform(Recno()))
	oCtrl.autosize = .t.
	oCtrl.caption = Alltrim(wObjShow.descri)
	octrl.left = 10
	octrl.top = lnTop + 3
	octrl.visible = .t.
	lntop = octrl.top + octrl.height

	oform.addObject('_'+Transform(Recno()), Iif(Empty(wObjShow.codice),Alltrim(wObjShow.ctrl),'p'+Alltrim(wObjShow.ctrl)))
	oCtrl = Evaluate("oform."+'_'+Transform(Recno()))
	oCtrl.width = 100
	octrl.left = 10
	octrl.top = lnTop 
	octrl.visible = .t.
	lntop = octrl.top + octrl.height
*-------------
* adding this line I haven't  errors anymore 
	Release octrl
*-------------
EndScan 	

Note that first of this step I cleared the oForm e oCtrl variables at the end of the program.
I also tried with clearing explicity each of the "OnFly Classes" but I kept on getting the same error.
Now it works !!

thanks for your support :)

>You can try to add
>

>CLEAR PROGRAM
>CLEAR CLASS ...
>

>
>In order to provide alternative you have to give more info on why you need to create a class on fly
>
>>I don't know why but I'm trying to define a class on the fly.
>>To do that I put the code on in a string, transform this string in a file.prg than compile it and add it to my procedures
>>
>>

>>lcString = myDefineCode
>>=strtofile(lcstring,MyFlyProc,0)
>>lcMemSet = set('procedures')
>>compile MyFlyProc
>>set procedure to MyFlyProc additive
>>
>>* excute my code which refers to defined object
>>release procedure MyflyProc
>>set procedure to (lcMemSet)
>>*
>>erase MyflyProc
>>
>>

>>
>>Well I cannot erase that file as it tells me that outstanding references exist. How can I kill those references
>>
>>Thank you
>>Alessio
>>
>>By the way, if there are better methods to do that...fell free to suggest them to me :)