Open project. File Download. Security Warning

[RBSTR]

Hi
When I open projects in Visual Studio and attempt to view a form view designer I have started getting "File Download - Security Warning" Message prompting a .tmp file in the location of my project.
Options to 'open', 'save' or 'cancel' do not lead to the view designer opening successfully.
If I close all open designers and rebuild the project I am then able to open the designers OK.
I saw a suggestion to 'restore file associations' in Visual Studio and tried this but with no success.
What might be causing this?
Thanks

 

[RBSTR]

Think I've sorted my problem.
I'm a bit of a newby so I may have been doing something stupid.
I saved and read through the .tmp file prompted.
It made reference to a build of a custom control I had created not being found on the form I wished to view.
I applied the latest build of the control and rebuilt the project and all seems to open OK.