ASP.NET IIS6, Forms authentication failed for the request. Reason: The ticket supplied was invalid

some of you may be familiar with this error and I've tried fixes, i've been bashing my head up a brick wall at this the past day and need some help from someone, somewhere :)

Situation:

I've got a website that was .NET 2.0 and we've recently released a new version with a major overhaul of functionality, in line with this, it's now in .NET 4, (Downgrading permanently back isn't an option unfortunately, won't go into detail though). Now, there's also a reporting services 2005 instance running on the box, and runs as a virtual directory, alongside the virtual directory for our shiny new .NET 4 app, there's a link from the new app to the reporting services, but now, when you click it, it asks you to login again, and that login doesn't work, it's as if I don't have the right permission/role, it accepts the login, then promptly does nothing, and when I check the event log, I get:

Event code: 4005 Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid. Event time: 3/14/2011 5:08:45 PM Event time (UTC): 3/14/2011 5:08:45 PM Event ID: 65061011ade64de69622f4a572cb0b25 Event sequence: 2 Event occurrence: 1 Event detail code开发者_运维问答: 50201

Now, it does use a custom authentication mechanism, but it all works in .NET 3.5 (Downgraded temporarily to check), but fails to work in .NET 4, I've tried making sure the machine keys are the same and change the reportserver, manager and the application so they all line up, but still nada.

So, I emplore you, can anyone help?

We have the same Auth cookie shared across several apps and suddenly ran into this error when we added a new app:

Event code: 4005 Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid.

Ends up our 'portal' app that manages users was .NET 4.0 and this new app was .NET 4.5.1, along with several others. This one offending app had this one extra line in the Web.config:

<httpRuntime targetFramework="4.5.1" />(Remove!)

All we had to do was take this out. But, we left in the line right above it for the compilation to be done in the 4.5.1 framework.