AxWebBrowser set_CSStyleSheet

[Richard Steele (Basemap)]

I have a win app that uses an embedded AxWebrowser control. At each page load
i require a different css file to be loaded and referenced. If I navigate
to 1 page then
back to the original I get the following exception, can any one help

Not enough storage is available to complete this operation.

then
Type: System.NullReferenceException
Message: Object reference not set to an instance of an object.
Source: PropertyBrowser
Stack Trace: at
PointandPress.PropertyBrowser.WebBrowser.set_CSSty leSheet(String value) in
c:\working\projects\current development\point&press\point & press for
property\code\propertybrowser_v2\propertybrowser_v 2\propertybrowser\webbrowser.cs:line 343
at PointandPress.PropertyBrowser.frmBrowser.CSStyleSh eet(String FileName)
--

the code to set the style sheet in the DOM is

[Browsable(true)] // Do not show in the properties box
[Description("Internet Explorer's CSS.StyleSheet Property")]
[DefaultValue("")] // Let the properties box know the default value
public string CSStyleSheet
{

set {document.createStyleSheet(value,0);}

{

Thanks
Richard