If your ASP.NET 1.1 or 2.0 application throws "This implementation is not part of the Windows Platform FIPS validated cryptographic algorithms" exception, the easiest way to fix is to add
<machineKey validationKey="AutoGenerate,IsolateApps" decryptionKey="AutoGenerate,IsolateApps" validation="3DES" decryption="3DES"/>
line to the <system.web> section of the web.config file of your application.
FIPS compliance is required for software installed on US government computers. The compliance requirement can be turned on and off.
Source: http://support.microsoft.com/kb/911722