If Internet Code Download fails to download a component, such as an ActiveX control, an error log is silently generated in the Temporary Internet Files folder. By default, this log is not generated if the download is successful.
When such a log is necessary for troubleshooting purposes, this log can be generated even for successful code downloads through the use of a special registry key.
When they error logs are created, they can be found as entries within the cache INDEX.DAT file:
The entries in Figure 1 show CodeDownloadErrorLog!Name with a corresponding CLSID or GUID. Sometimes an Internet search will reveal information about the CLSID or GUID, providing further information as to their use. The following table relates to the CLSID values for the URLs above.