The following information may help you further in finding the correct item(s) - it's a list of useful searches/filters.
This is not a complete list, but it does cover several of them.
Asset KUID - This is useful if you have a specific KUID, or list of KUIDS causing issues. This one is frequently added if you use View Dependencies or View Dependent Assets followed by View in Main List.
Author - This is useful to find assets by a particular author.
Built-in - as it says on the tin effectively, it shows built-in content if set to True.
Category - As explained above, this is used for selecting specific categories. If you need to select more than one, use the AND or OR options near the bottom of the list.
Date Installed/Modified - this can be used to find assets created, installed (i.e. added from a .cdp file or from the Download Station) or modified on a particular date. If used with Download Station assets, the Date Installed is usually the date it was added to the Download Station.
Faulty - If set to True, this will search for faulty assets. If False, this excludes faulty assets.
Faulty Dependencies - same as above, but this will tell you which assets have a faulty asset as a dependency.
Has Warnings - Similar to Faulty, this displays assets with warnings. Normally warnings will not affect the performance of Trainz.
Locally Modified - This shows assets that have been modified. This may be by opening for editing and recommiting, or it may be installing assets from a .CDP file (from another website)
Location - This is used to select where you want the search results to be showing assets from - Local is on your system, Download Station is as it says - the DLS, you will probably not need to worry about the other two.
Minimum build version - this is used to find assets that were made in a particular version or above. This one is a bit tricky to use until you are famillar with the trainz-build tag.
Missing Dependencies - used to identify assets with (as the name states) missing assets.
Open for Edit - this is for assets that need to be committed to add them to the database.
Obsolete/Out of Date - these are asset states, to indicate whether you have a newer version installed (Obsolete) or there is a newer version available (Out of Date). Best used with Location - Local.
Scripted - identifies assets which have scripts attached to them.
The items below this can be used to add and, or, and not criteria to the search.
There are a few others, but these are the useful ones.
Hopefully this helps.
Shane