browser login error

I am trying to display a crystal report in an aspx page. I created the page, the report viewer and then the crystal report as crystalreport1. I then set the reportviewer.reportsource to a new instance of crystal report1. I am accessing data from a SQL server db that I am already logged into. If I create and try to access the same report using a regular windows app, it works. When I try to build and browse the app it gives me the following error:

Any ideas why?

Logon failed.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: CrystalDecisions.CrystalReports.Engine.LogOnException: Logon failed.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[LogOnException: Logon failed.]
.K(String
, EngineExceptionErrorID ) +546
.F(Int16 , Int32 ) +491
CrystalDecisions.CrystalReports.Engine.FormatEngine.GetPage(PageRequestContext reqContext) +459
CrystalDecisions.ReportSource.LocalReportSourceBase.GetPage(PageRequestContext pageReqContext) +189
CrystalDecisions.Web.ReportAgent.v(Boolean `) +150
CrystalDecisions.Web.CrystalReportViewer.OnPreRender(EventArgs e) +108
System.Web.UI.Control.PreRenderRecursiveInternal() +62
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Control.PreRenderRecursiveInternal() +125
System.Web.UI.Page.ProcessRequestMain() +1470

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Version Information: Microsoft .NET Framework Version:1.0.3705.0; ASP.NET Version:1.0.3705.0