With some repos or sometimes (I don't know), searching the working copy does not work. Using the "Search" widget to search the WC for a word like "keep" causes nothing to happen except for the status bar to show the following: "path contains illegal component: [ ] Searching 0 / 939 files". Nothing more of the error message is visible. The "[ ]" denotes an empty progress bar. My WC path is something like "E:\WCs\company\productA".
I did not get a longer or other error message, even though I tried this: Setting ui.traceback=1 and tortoisehg.guifork=False in the mercurial.ini, then launching "thg.exe --nofork" from the commandline after having "set THGDEBUG=1".
[THG 2.9.2 on Win7 32-bit.]