problem decoding authentication request message

[Steven Carmody]

Hi,

I'm currently testing a non-Shib SP; I'm using IDP 2.3.x.

The first time I go to this SP and get redirected to my IDP, I get this 
in my idp logs:

Error decoding authentication request message

Then, if I just hit the SP again (immediately), things work as expected.

I'm sure this isn't a Shib problem --

BUT, any suggestions as to how I might capture the authentication 
request messages, so that I could send them to the other vendor ?

I'm using this profile:

profile/SAML2/POST/SSO


Thanks!