Update: Add the following line after Report form..

oPrintPrev.release()

>Dear Sir,
>
>I wrote your following codes on command button
>

>oPrintPrev.visible=.F.
>oPrintPrev=.NULL.
>release oPrintPrev
>

>While viewing report when I click command button it show following error message
>

>Object oPrintPrev is not found
>

>
>please modify codes again