What follows is a lengthy excerpt of a problem caused by a BHO (Browser Helper Object) distributed from Ziff Davis Publications  and a possible solution that may give you more insight in troubleshooting BHO problems.

ZDNet Magic InstaFiller uses an Internet Explorer Browser Helper Object (also called an IE BHO) to obtain information about the current form or forms being displayed.  A BHO is a Dynamic Link Library DLL, loaded by Internet Explorer when the user launches the browser. You can have several BHOs on your system, some installed automatically when you install software that interacts with Internet Explorer.  Most of the time, under IE 4.0, a failure in loading one BHO does not adversely affect other BHOs (although it could occur). However, IE 5.0 seems to stop loading all other BHOs. Thus, you need to examine the registry location where BHO data is stored and verify that the entries are correct. The following instructions require using the Registry Editor. Please follow these steps EXACTLY. You can severely affect the operation of the Windows Operating System if you delete Registry Keys--this includes the possibility of making the machine not bootable, or requiring the re-installation of Windows, and possibly the loss of all data on your hard drives. DCI and the Program Author are not responsible for any damage to users' machines due to working in the registry. You should do this at your own risk. However, if steps are followed exactly, there shouldn't be any problems at all. Follow these steps exactly and in order to determine the Browser Helper Objects loaded on your machine: Close Internet Explorer. If using Windows98, close Control Panel, Windows Explorer, and any windows opened from clicking on "My Computer". Launch The Registry Editor by clicking Start Run. Type the following: regedit. Double click on the following Registry Keys appearing in the left-hand panel of the Registry Editor (You may need to scroll to locate these keys; they aren't case sensitive): HKEY_LOCAL_MACHINE | SOFTWARE | Microsoft | Windows | CurrentVersion | Explorer | Browser Helper Objects. You will now see either one or more CLSID entries (long series of numbers/letters). The ZDNet Magic InstaFiller BHO is: {BC5C39A5-9F26-11D2-B776-004005429A8A}. To verify that another BHO is conflicting with ZDNet Magic InstaFiller, do the following: a. Single click (i.e. select) on where it says "Browser Helper Object" in the left pane. b. Select the Menu item: Registry-Export Registry File c. In the "Export Registry File" dialog box, make sure "Selected Branch" is selected d. Save the current contents of "Browser Helper Objects" and all subkeys in a file on your local hard drive, it will have an extension of .REG, for example save it as: C:\BHO_KEYS.REG This is so that you can re-load these keys later. e. Click the Save Button f. While Registry Editor is still open, Launch Windows Explorer to verify the file has been saved. Close Windows Explorer. g. **IMPORTANT** In the Registry Editor, MAKE SURE that what you have highlighted (i.e. selected) reads: "Browser Helper Objects" and press the DELETE Key. This will delete "Browser Helper Objects" and all its subkeys, including the Magic InstaFiller subkey mentioned above {BC5C39A5-9F26-11D2-B776-004005429A8A}. h. Respond Yes to the prompt, and then close the Registry Editor. ZDNet Magic InstaFiller will automatically re-insert its own Registry Key when it's launched again. Launch Magic InstaFiller and IE 5.0 in the exact order specified below. This order is important for the first time you use InstaFiller as the BHO Registry Key has to be created first. a. Launch ZDNet Magic InstaFiller b. Launch Internet Explorer. You should now be able to fill in Web Forms. If ZDNet Magic InstaFiller still doesn't work at this point, you will need to go back to the Registry Editor and remove the Browser Helper Objects subkeys one at a time--from top to bottom underneath "Browser Help Objects." Do this by following steps 4a through 4h, but instead of deleting the entire "Browser Help Objects" key and its subkeys, select and delete the first (topmost) subkey under it as step 4a then follow through step 4h. Begin with all steps again with the next subkey, and so on. Some other applications' Browser Helper Objects registry keys will need to be re-established. To Re-load their Registry keys, use Windows Explorer to locate the file you saved in step 4e and double click on it. It will automatically reload. Auto-reload of keys: Save the BHO keys into a .REG file as mentioned in step 4d above. By double clicking this file in Windows Explorer, the association of this file with the Registry editor will automatically re-load all of the keys you have deleted. To reload ZDNet's Magic InstaFiller registry BHO key, just launch the program and its BHO key will be reloaded without having to double click in Windows Explorer.