>>I haven't restarted my computer yet. Tomorrow I let you know, if the problem would still exist. Do you have suggestions to solve this problem? Anyone has seen this behavior? Looks like JavaScripts on my computer sometimes work incorrectly. At least, I noticed similar behavior on other sites, which work fine from other computers.
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>>The problem is really frustrating. Imagine every 5 min. or so messagebox pops up the screen...
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>Yes, this would certainly be frustrating. I don't know how to resolve. I also have some issues like this sometimes and windowsupdate.com, update of Virus and other tools, clear cache, restart computer and such is what I do.

Thanks, Michel. The problem seems to disappear by its own. Right now everything is Ok.