What browser are you runing?
What permssions do you have on your W7 box and you have the anoying windows UCE turned off.
A suggestion, clear all browser cache files and reset IE to default. Then uninstall your java both x32 and x64. Reboot, install Firefox. Install java for both IE and Firefox for plugins.
On IE 9 make sure that you have compatibility mode set and running for the url of your proxmox box. You my even want to put the url for the proxmox server on the trusted site and drop all permssions to low for trusted site and put the certificate in trusted site.
Turn off all antivirus and turn off Windows Defender. Quite often you can have overlapping antivirus on a windows 7 box and I have seen for example Kasparksy and Windows Defender conflict and create some interesting problems when browsing sites.