Hi there. Have you made sure that you have changed the setup so that it kicks off in IE6. I know that the latest version of ST did have a few issues with IE7 but i think they were rolling out a patch to resolve that. You may also have to look at the config files.
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It's not working even after re-installation,
I have tried by creating a new project too.
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Open IE7. Click Tools->Managed Add-ons->Enable/Disable add-ons. In the popup, Verify QAPHlprObjClass is enabled or not. Then verify whether IE7 extension is enabled in Enabler extension and your project.
If any of above methods are not working, can you try with other local user in that machine? DLLs might be corrupted..