If you get a Http 405 error while trying to validate the workflow url in AX you are probably running into a static file handler issue. You can verify this by going into IIS to the workflow web site, find the axworkitems.asmx within that website, right-click on it and choose Browse. If you get this error: "HTTP Error 404.17 - Not Found. The requested content appears to be script and will not be served by the static file handler" you definitely have a static file handler issue.
This usually occurs when you have the 4.0 .NET framework installed on the machine. The workflow web services are built with version 2.0 of .NET. IIS has associated the workflow web service files with the 4.0 file handler and the services are not functional with that handler.
To correct the issue, create a new application in IIS under the your Workflow site. Point the new application to the Program Files\Dynamics AX\50\Workflow folder. Set its application pool to the MicrosoftDynamicsWorkflow50 application pool. After doing this the issue should be resolved. The newly created application will have WebServiceHandlerfactory-ISAPI-2.0 Handler Mappings whereas the previous one had only one mapped to Asp.NET 4.0.
I tried the solution above with no luck. I am using Sharepoint 2010.
For Sharepoint 2010 there is a hot fix that is required that might be giving you grief...not sure if you have this or not:
Microsoft SharePoint 2010 is supported with Microsoft Dynamics AX 2009 Service Pack 1. If you plan to use SharePoint 2010, you must download and install the hotfix package available with Microsoft Knowledge Base article number 2278963.
Also have a look at this site to see if this helps you out:
Ty Becky :)