Login erratic with Internet Explore Eight

For some time now login to our Adobe Connect Pro server has been erratic from my main home machine—Vista 64-bit using Internet Explorer 8, 32-bit version. Sometimes it works but most of the time it doesn't. Meantime, I can login just fine from Firefox on the same machine and system—consistently.

Does anyone have any idea what might be going on here? Rebooting doesn't seem to fix the problem—at least not right away.

Thanks in advance for any help!