I have a date field in my DB, however I didnt realize the originating data in excel had some of the dates backwards...

02.03.2009 should be 03.02.2009, but not all dates are broken like this so I want to do an update on the date field but it wont let me...

UPDATE [FEB] SET [FEB].[Date] = #2/3/2009#
WHERE ((([FEB].Date)=#3/2/2009#));

why wont this work?

OPERATION MUST USE AN UPDATEABLE QUERY

Date is a reserved word in access and since you have named a field Date, it must be surrounded with [] every time you reference the [Date] field.

you should be better of if you rename the field eg dtDate use format for checking and changing the date order.
Further it seems that whateve way you format Access stores the dates in YYYY-MM-DD format, so best approach would be to store the dates in YYYY-MM-DD format and display in queries, forms, report etc as you desire.

No Access stores dates as a number of (integer) ticks for (IIRC) 01/01/1900, it stores times as the number of seconds from midnight (as decimal) so the integer part of a datetime tells you the day/month year, the decimal part the time. when you request a vlaue form a datetime value, unless you specify the format it will be returned in the default short time format as per your systems localisation settings.

I would agree that generally you are better presenting dates to the system as per the ISO standarad as year month day, or the US standard dd/mm/yyyy. Access is quite keen on identfying dates with a has symbol eg #03/08/2009#

going back to the OP
Date is a reserved word and you will have problems over time using a reserved word.. reserved word being a word that JET SQL 'reserves' for its own use. if you do a google on MS Access reserved words you will find plenty of help on what not to use. Why db authors and tool developers don't block attempts to use reserved words is beyond me. JET does do a very good job trying to workaround use of reserved words but occasionally it does come a cropper

instead of
UPDATE [FEB] SET [FEB].[Date] = #2/3/2009#
WHERE ((([FEB].Date)=#3/2/2009#));
try
UPDATE [FEB] SET [FEB].[Date] = "#2/3/2009#"
WHERE [FEB].Date="#3/2/2009#;

Im assuming that your column 'date' actaully is a date time value
Im also a little horrified to think that your table is called 'Feb' and you have 11 other tables called Jan, Mar,Apr...Dec... that has the firm smack of bad design

A link where MS describes a DateTime field.
Another link I use for reserved words.