Why do I keep getting prompted to install the ChemDraw ActiveX control when using the ChemACX web site even though I already have it installed?
IE8 and IE9 users must add the ChemACX website to the list of trusted sites for IE.
To do so, open up IE and select Tools > Internet Options > Security tab.
Select the Trusted sites zone, click on Sites, and add the following URLs to the form: https://chemacx.cambridgesoft.com and http://chemacx.cambridgesoft.com (note you will have to uncheck the “Require Server verification…" checkbox to add http sites to this list).
Restart your browser and you will be able to access the site again without the error.