sql - mysql crashes when alter table -

i using mysql version 6.1.4 , windows 7

i have empty table want drop column , foreign key. when try apply changes workbench crashes , when try stop mysql returns error

error 2013: lost connection mysql server during query sql statement: alter table `teste_db`.`search_products`  drop foreign key `product_id_id_refs_id_aa2f4dab`     error: error when running failback script. details follow.  error 2006: mysql server has gone away 

i have looked around lot , not find clue...

thanks in advance help!

please follow steps , if dont

1. if myisam table repair first , check table .
2. where empty table , check if index present delete that,

try , if still not work

please paste table structure , table engine name.