problems with mysql database

[David Banning]

I have recently converted from mysql 4.1 to 5.0 and some of my
tables are not recogized. Using the mysql_upgrade utility is
not effective as -it- does not recognize certain tables. 

On closer examination I see that the tables that are -not- recognize
have the following extensions;

-rw-rw----  1 mysql  mysql  147787 Jul 23 02:44 company.ISD
-rw-rw----  1 mysql  mysql   13312 Jul 23 02:44 company.ISM
-rw-rw----  1 mysql  mysql    9064 Dec  8  2006 company.frm

while the tables that have no problem have different extensions;

-rw-rw----  1 mysql  mysql  3592 Jul 28 23:49 Employees.MYD
-rw-rw----  1 mysql  mysql  1024 Jul 28 23:49 Employees.MYI
-rw-rw----  1 mysql  mysql  9174 Dec 19  2006 Employees.frm

Any idea whats going on here?