Hi Dick,
KUID searching can be a bit complex depending on method, but there are a few tricks that can help.
For searching using Content Manager, you need to use the < > marks - it's only when using the old 'black pages' version that you do not need these.
If you only have the author part of a KUID, though, you can search for this using Author rather than Asset KUID, then enter # followed by the author's ID if you do not know their username.
Shane