Looks like a bug to me - the PageFrame.Resize() is firing before the contained objects' init()s.
To work around this, you can check for the object's existence first, e.g.

With This.page1
  If Type(".text1.width")="N"
    .text1.Width=100
  EndIf
EndWith

>Visual FoxPro 08.00.0000.3117 for Windows
>Windows 5.01, build 2600, Service Pack 1
>
>1) CREATE FORM test
>2) Add PageFrame1 object
>3) Add PageFrame1.Page1.TextBox object
>4) Modify PageFrame1.Resize Event as follows:
>

>WITH THIS.Page1
>	.Text1.Width=100
>ENDWITH
>

>5) Run the form -- receive no error.
>6) Set PageFrame1.Page1.FontSize to 12
>7) Run the form -- receive an error "Unknown member TEXT1"
>
>Please try the steps above. I just wonder may be something is not Ok with my computer's settings. Or my own ones on January the 2nd :(