Data type resulted in an out-of-range datetime value.

declare @evdatetime varchar(100)
set @evdatetime = '01/10/10 - 08:57'
select convert(char(8), @evdatetime, 12)


This works for the value in your sample.
I suspect there are other rows in the data that cannot be converted, but it won't be easy to find them.

this be in the form of a store proc? can you embellish?

Provide more data to figure out error.
You can provide data in Excel sheet.

Herewith the source field and target (in red)
Sample.xls

update dbo.dataset set eventdate =
Convert(DateTime, Left(EventDateTime,2) + '-' + Left(DateName(mm,  '01' +  '-' + Substring(EventDateTime, CHARINDEX('/', EventDateTime) +  1, 2) + '-' + Right(EventDateTime,2)),3) + '-' + Right(EventDateTime,2) , 103 )

See above querty is working or not

update dbo.dataset set eventdate =
Convert(DateTime, Left(EventDateTime,2) + '-' + Left(DateName(mm,  '01' +  '-' + Substring(EventDateTime, CHARINDEX('/', EventDateTime) +  1, 2) + '-' + Right(EventDateTime,2)),3) + '-' + Right(EventDateTime,2) , 103 )

See above query is working or not

wait little change Replace EventDateTime WIth CONVERT(CHAR(8),eventdatetime,12)

Is there anything less messy than the above solution?

Ya above one is little messy but u just try it on your sample table. U have to execute the below query and let me know it is working or not

Update dbo.dataset set eventdate = Convert(DateTime, Left(EventDateTime,2) + '-' + Left(DateName(mm,  '01' +  '-' + Substring(CONVERT(CHAR(8),eventdatetime,12), CHARINDEX('/', CONVERT(CHAR(8),eventdatetime,12)) +  1, 2) + '-' + Right(CONVERT(CHAR(8),eventdatetime,12),2)),3) + '-' + Right(CONVERT(CHAR(8),eventdatetime,12),2) , 103 )

I will give it a spin in the morning. ta

@svalekar works. but i was hoping for something more elegant. if i don't get one by the cob today i will award the points to svalekar.

i am in sydney, the time right now is 8:26 am.

Perhaps something like this:
CONVERT(datetime, LEFT(EventDateTime, 8), 1)

Or if you want to time as well:
CONVERT(datetime, REPLACE(EventDateTime, '-', ''), 1)

The full statement goes like this for the date portion:

Update dbo.dataset set eventdate = CONVERT(datetime, LEFT(EventDateTime, 8), 1)

Mr. SQL Server said this:

Msg 8115, Level 16, State 2, Line 1
Arithmetic overflow error converting expression to data type datetime.
The statement has been terminated.

Nice try. Sorry I would have liked it to have worked.

It looks like you are now using MDY but rather DMY, therefore you should use:
UPDATE  dbo.dataset
SET     eventdate = CONVERT(datetime, LEFT(EventDateTime, 8), 3)

And that should have read:
It looks like you are not using MDY but rather DMY,

That's correct. And this works as a read, SELECT CONVERT(CHAR(08), eventdatetime, 101) FROM dbo.dataset, but when I incorporate into an update I get an out of range.

I tried this: update dbo.datasset set eventdate
 = CONVERT(datetime, LEFT(EventDateTime, 8), 3)

I got this:

Msg 241, Level 16, State 1, Line 1
Conversion failed when converting datetime from character string.

spot on. thanks for the tip. 5 lines of rubbish crept into the file.