People like you and me ask and answer questions in Yahoo! Answers. It doesn't look like Yahoo is supporting their toolbar because Yahoo provides no means to submit problems regarding the Yahoo toolbar. You should get in the habit of providing configuration details in your Yahoo Answers questions. You don't say what browser (IE 8, IE 9, IE 10, Firefox) you are using. You don't say what OS (XP, Vista, Windows 7 or 8) you are using. You don't provide the exact message text for the script error. I did some searches and I could only find one thing that looked promising. No guarantees. I assume you are using IE 9 as your browser. Click the white gear icon near the upper right corner of your browser and click Manage add-ons. On the left side under Add-on Types click Search Providers. Under Name you should see Bing. If it is not the default, then click it and set as Default. Then click the other search provider names one at a time and click Remove. Enable the Yahoo toolbar and see if that fixes the problem. The theory is that you have a search provider that is creating an error and that error is propagating to the Yahoo toolbar. If that doesn't work, then I am clueless.
You might try using the Yahoo toolbar under Firefox as a workaround.