It sounds like your web.config file is missing a SafeControl entry? You should have the following SafeControl tags in your web.config file. Can you verify this?
<SafeControl
Assembly="SPSolutions.SharePoint, Version=1.0.0.0, Culture=neutral, PublicKeyToken=08a33cc09f006379"
Namespace="SPSolutions.SharePoint.WebControls"
TypeName="*" Safe="True" />
<SafeControl
Assembly="SPSolutions.SharePoint.AlertManager, Version=1.0.0.0, Culture=neutral, PublicKeyToken=08a33cc09f006379"
Namespace="SPSolutions.SharePoint.AlertManager.ApplicationPages"
TypeName="*" Safe="True" />
<SafeControl
Assembly="SPSolutions.SharePoint.AlertManager, Version=1.0.0.0, Culture=neutral, PublicKeyToken=08a33cc09f006379"
Namespace="SPSolutions.SharePoint.AlertManager.WebControls"
TypeName="*" Safe="True" />