window 7 32 bit client machine dot net exe running in IE8 or IE9 from server security warning file download issue

Help me in the issue, Asp dot net exe which run from server in IE 8 window 7 32 bit client machine show security file save download message. This app was running fine if we don't apply any window 7 or IE8 patches. same issue when running in IE9. I already run the caspol, add the server link to trusted site with low security. I wonder why it was working fine without any patches.
I just found that client machine win 7 32 bit has dot net 4.5.1 installed when updated all the patches. after uninstall the dot net 4.5.1. the application worked fine. now I wonder what are the settings need to change to run the application with dot net 4.5.1 installed on machine. as Microsoft always has these things in window updates. thanks in advance.