We've seen this one before – and there's a Microsoft KB article on it here but in the KB they don't mention any ways to resolve this issue.
Error Message: The list cannot be displayed in Datasheet View for one or more of the following reasons:
-A datasheet component compatible with Windows SharePoint Services is not installed.
-Your web browser does not support ActiveX controls.
-Support for ActiveX controls is disabled.
Background: You will see this message displayed if you use FireFox, Opera, Safari or any browser other than Internet Explorer 6.0 – 7.0. Using Data Sheet View in WSS 3.0 or MOSS 2007 allows you to easily edit your SharePoint lists in a familiar spread-sheet-esque manner. This is not to say that it is a fully functioning web spreadsheet as in Excel Web Access (Excel Services). If you're having issues using the Data Sheet View there are several prerequisites you need to meet before you can use this SharePoint feature.
- You must be using a PC
- You must be using IE 6 or higher
- You must enable certain ActiveX security settings.
Some anecdotal evidence also suggests is a good idea, though not necessary, to have the Windows SharePoint Service Support options for Microsoft Office installed. Skip to step 5 if you don't want to do this. Here are the instructions for Office 2007. To verify that these components are installed and available go to Start > Control Panel > Add or Remove Programs > click on Microsoft Office and then Change. You may need your Office 2007 install media beyond this step.
Follow the steps for changing your Microsoft Office installation.
Expand the Office Tools category.
Next verify that you have both the Microsoft Office Access Web Datasheet Component and the Windows SharePoint Services Support component installed.
If these components are not installed choose to run them from your computer and then click the Continue button and go through the installation process. You may need your Office 2007 install media.
Next you want to verify that you can run ActiveX controls in Internet Explorer. To do this open IE and go to the Tools menu > Internet options.
Next click on the Security tab and for your Trusted sites click (choose Internet if you do not add your SharePoint sites to your Trusted Sites) on the Custom level button (both examples shown below as 6 and 6A).
OR
Verify that you can use previously unused ActiveX controls.
Verify that you can download signed ActiveX controls and that you can run ActiveX controls and plug-ins.
The next setting is very critical – select "Enable" for Script ActiveX controls marked safe for scripting.
Adjust these settings accordingly and then click OK twice to return to Internet Explorer.
You may need to close Internet Explorer and re-open the program before your new settings take hold and become active. This will resolve the issue in about 95% of the cases out there.