The error happens with password-protected MS Office documents. We use the MIP plugin to do some file type analysis and it is returning an error, in this case, that we should be ignoring. After this, our code will use other plugins to determine the file type, and these files will be correctly identified by those plugins despite this error. This is new in 15.8 because we added in some metric collection on various errors during detection and this is one of the included errors
Release : 15.8
Component : Network Prevent for Email/Web/Endpoint
The event can be ignored; this will be resolved in a future release of DLP.
This issue can be worked-around by disabling the MIP plugin on the Detection Server. This is done by editing the MIP plugin's manifest.xml file
and changing the text disabled="false" to disabled="true" and restarting the Detection Server.
This, of course, will also disable the Detection Server's MIP support.