One problem I see is that the retURL needs to be URL encoded so that when it is passed in the URL it is interpreted correctly.  There cannot be characters like “/” or “?” in the retURL value - because those will get interpreted by the browser as part of the base URL rather than as part of the retURL parameter. 

A more appropriate URL encoding for the returl would be somthing like this. 

%2Fapex%2Fskuid__ui%3FCaseId%3D{{$Param.CaseId}}%2Fpage%3DCaseDetailsModel

I know that looks like ugly code that would be impossible to remember.  We use a cheater URL encoder tool  (like this:  http://meyerweb.com/eric/tools/dencoder/) when building pages.  

In addition the merge fields  - {{$Param.CaseId}}  shouldn’t be URL encoded because they get replaced with real values before being sent to the browser.  If you did URL encode them the merge wouldn’t work…

Hope that helps. 

Thanks Rob I have built this for the URL:
/p/attach/NoteAttach?pid={{$Param.CaseId}}&retURL=%2Fapex%2Fskuid__ui%3FCaseId%3D{{$Param.CaseId}}%2Fpage%3DCaseDetailsModel

It goes to the attach file Salesforce page and then redirects me to this URL:
https://skuid.cs18.visual.force.com/apex/ui?CaseId=50011000003AQptAAG%2Fpage%3DCaseDetailsModel

and I get this error:
You’ve been INKED! (Something went wrong)
Skuid was unable to redirect the user to standard Salesforce Page Layouts, and no Skuid Page could be used instead.

as the page=CaseDetailsModel prob isn’t correct, can you suggest anything.

Thanks

Edward

Rob, You really need to pull this great information into the tutorials / developer doc. I needed this information and start in the doc first.

You are right Irvin.