I am using 4.0.14-max-debug and have more than a dozen innodb and haevn't had any problems except now when i am trying to change the structure of a table.

I successfully created the tuning table with a FK referring to program table. I added an additional programvehicle table with a prgid. The programvehicle table with FK for program table. Now i want to drop the FK for program from tuning and instead add FK for the id of programvehicle. However, i cannot remove the foreign key. I get the following error messages :
------------------------------------------------------------------
mysql> alter table tuning drop foreign key;
ERROR 1005: Can't create table '.\tuningdb1\#sql-304_5.frm' (errno: 150)

mysql> alter table tuning drop column prgcode;
ERROR 1025: Error on rename of '.\tuningdb1\#sql-304_5' to '.\tuningdb1\tuning'
(errno: 150)

mysql> alter table tuning drop index progcode;
ERROR 1091: Can't DROP 'progcode'. Check that column/key exists

mysql> alter table tuning add index(progcode);
ERROR 1072: Key column 'progcode' doesn't exist in table

-----------------------------------------------------------------------------

The strange thing is that when i do a show columns in can see progcode which is a key :

mysql> show columns from tuning;
+---------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+------------------+------+-----+---------+----------------+
| tid | int(10) unsigned | | PRI | NULL | auto_increment |
| tname | varchar(15) | YES | | NULL | |
| ttype | varchar(10) | YES | | NULL | |
| tlocation | varchar(10) | YES | | NULL | |
| last_modified | timestamp(12) | YES | | NULL | |
| tspkprefix | text | YES | | NULL | |
| tdulos | text | YES | | NULL | |
| tcomment | text | YES | | NULL | |
| tsrc | varchar(15) | | | | |
| huid | int(10) unsigned | YES | MUL | NULL | |
| prgcode | varchar(5) | YES | MUL | NULL | |
| tdate | date | YES | | NULL | |
+---------------+------------------+------+-----+---------+----------------+
12 rows in set (0.00 sec)

Well, I don't user ALTER TABLE (I just DROP and reCREATE
my tables), but I see three problems.

The MySQL documentation for 'alter table <table> drop
foreign key ...' says you should use this syntax:

ALTER TABLE yourtablename DROP FOREIGN KEY internally_generated_foreign_key_id

Which means you left out the name of the foreign key.
You can see this constraint name by doing a:
SHOW CREATE TABLE <tablename>;

The second problem is a simple typo:
you are referencing the field 'prgcode' with 'progcode'.

A third problem is you didn't set field 'prgcode' to 'NOT NULL'.
(You are allowing NULLs in an index field.)

-lv