Error Code:1028 Sort aborted - after moved mysql DBs (

I moved the MySQL databases from c: to e: disk
Change MY:
[mysqld]
datadir=e:\mysql_databases

and

SELECT * FROM forums WHERE post REGEXP 'blabla'  ORDER BY RAND() LIMIT 5

Code (markup):

stopped working (
without 'ORDER BY RAND()' perfect work.

any advice please.