R – MOSS 2007 and Sharepoint desinger

You'll have to use an event handler if you want to validate the state of multiple fields. You can use the ItemAdding/ItemUpdating events if you want to cancel an item which is being added/updated.

properties.Cancle = true; properties.ErrorMessage = "Your validation message.";

http://msdn.microsoft.com/en-us/magazine/cc163318.aspx

http://blogs.msdn.com/brianwilson/archive/2007/03/05/part-1-event-handlers-everything-you-need-to-know-about-microsoft-office-sharepoint-portal-server-moss-event-handlers.aspx

Open you web.config file of the SharePoint web Application, search for CallStack change it to true and seach for CustomError and set its value to Off. Do the action again you will get to know the actual error causing the error. Rectify it or post the error that will help to point out the issue.

Also notes in case of STP,

1. If have some LookUp field in the List template, you will need to recreate those fields again or Follow the workaround as described in article
2. If you have created any Site Column make sure that is there in the new site collection as well.