The security validation for this page is invalid. - SharePoint 2010

In my case I got this error while activating a feature. You might encounter this error during Feature activation using power shell script or STSADM. The exact error message would be follows

The security validation for this page is invalid. Click Back in your Web browser

, refresh the page, and try your operation again.        

Solution : You need to make sure you have set the AllowUnsafeUpdates to false somewhere in the feature activation code and your code expect it to be true to perform certain actions. You may change it back to False at the end of the feature receiver code.

An unexpected error occurred. Error 19106. - Performancepoint Dashboard Designer not working

When you try to access PP dashboard designer from BI Tools in SharePoint 2010 you get-

"The URL is not available, does not reference a SharePoint site, or you do not have permission to connect"

I fixed the above issue by trying following things in order

1. Recycle the app pool running the Performance Point service.

2. Restart the PerformancePoint service from central admin

3. Perform an IISRESET.

Please note in my case Designer Dashboard was working earlier and had stopped suddenly. If you are setting it up for the first time then you need to configure the performance point services to use this as Unattended Service Account to access data sources in service application settings in central admin.