Did you reinstall PlecoDict using the "automated" or "manual" installer? If you used the manual one, did you make sure to install the data files from the "Handwriting Recognizer" folder, and install them to your Palm's internal memory (and not to an SD card)?
Anyway, to fix this, download another "manual" copy of the PlecoDict demo version from
http://www.pleco.com/palmdownload.html, open it, and double-click on each of the files in the "Handwriting Recognizer" folder to queue them up to install to your Palm, then HotSync your Palm with your PC and the files should copy over.
If you encounter an error mesage during HotSync, or if the handwriting recognizer still doesn't work after reinstalling those files, go into your Palm's "Delete" screen and see how much free memory you have - if it's less than 1.5 MB or so, delete some files and try again.