New Post: Getting Error when ToolsVersion value is set to 4.0

We are receiving the following error when ToolsVersion value is set to 4.0. It works when I remove ToolsVersion value ( default is 2.0) on my computer. Can someone please help me understand what is happening behind?

C:\Program Files (x86)\MSBuild\DeploymentFrameworkForBizTalk\5.0\BizTalkDeploymentFramework.targets(1744,5): error MSB4062: The "Microsoft.Sdc.Tasks.BizTalk2006.Application.Delete" task could not be loaded from the assembly C:\Program Files (x86)\MSBuild\DeploymentFrameworkForBizTalk\5.0\Microsoft.Sdc.Tasks.BizTalk.dll. Could not load file or assembly 'file:///C:\Program Files (x86)\MSBuild\DeploymentFrameworkForBizTalk\5.0\Microsoft.Sdc.Tasks.BizTalk.dll' or one of its dependencies. The system cannot find the file specified. Confirm that the <UsingTask> declaration is correct, that the assembly and all its dependencies are available, and that the task contains a public class that implements Microsoft.Build.Framework.ITask.

Thanks!
Pavan