Invalid SQL: ALTER TABLE userfield CHANGE field1 field1 MEDIUMTEXT NOT NULL

[Steve Machol]

Handling via a support ticket. This was due to a change made to his database.

[Junior]

Database error in vBulletin 3.0.1:

Invalid SQL: ALTER TABLE userfield CHANGE field1 field1 MEDIUMTEXT NOT NULL
mysql error: BLOB column 'field1' used in key specification without a key length

mysql error number: 1170

Date: Friday 10th of September 2004 09:41:41 AM
Script: [url="http://board.raptalk.net/install/upgrade13.php?step=3"]http://board.raptalk.net/install/upgrade13.php?step=3[/url]
Referer: 
Username: Junior
IP Address: 67.125.193.51

I am getting this error when trying to upgrade form VB 3.0.1 to vb 3.0.3 on Step 3) Miscellaneous table alterations 3/4 (Step 3 of 9)

Please help. Already tried running myisamchk on it. Any suggestions?