Pull between 2 dates from user input

I want to pull dates from my database that are between to set dates i have written a query that does this which looks like this:

"SELECT OCH_ID, empno, Selected_OCD, Start_Time, End_Time, Selected_OCDay, Selected_DOM, Selected_Month, Selected_Year FROM dbo.ICT_On_Call_Hours WHERE (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) >= CONVERT (datetime, LEFT ('12/02/2007', 2) + '/' + SUBSTRING('12/02/2007', 4, 2) + '/' + RIGHT ('12/02/2007', 4))) AND (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) < CONVERT (datetime, LEFT ('14/02/2007', 2) + '/' + SUBSTRING('14/02/2007', 4, 2) + '/' + RIGHT ('14/02/2007', 4)))"

This works when the dates are included in the statement but when i try and use parameters to pull them in like this:

"SELECT OCH_ID, empno, Selected_OCD, Start_Time, End_Time, Selected_OCDay, Selected_DOM, Selected_Month, Selected_Year FROM dbo.ICT_On_Call_Hours WHERE (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) >= CONVERT (datetime, LEFT ('@.Choice1', 2) + '/' + SUBSTRING('@.Choice1', 4, 2) + '/' + RIGHT ('@.Choice1', 4))) AND (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) < CONVERT (datetime, LEFT ('@.Choice2', 2) + '/' + SUBSTRING('@.Choice2', 4, 2) + '/' + RIGHT ('@.Choice2', 4)))"

I then recieve the following error message why is this?

ERROR ------> Syntax error converting datetime from character string.

Any Help would be greatly appreciated thanks

Dont surround a parameter with single quotes. Also if choice1 is a data already why not try something like this

"SELECT OCH_ID, empno, Selected_OCD, Start_Time, End_Time, Selected_OCDay, Selected_DOM, Selected_Month, Selected_Year FROM dbo.ICT_On_Call_Hours WHERE (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) >=@.Choice1 AND (CONVERT (datetime, LEFT (Selected_OCD, 2) + '/' + SUBSTRING(Selected_OCD, 4, 2) + '/' + RIGHT (Selected_OCD, 4)) <@.Choice2"

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Thanks for the immediate response that works perfectly exactly what i wanted

Thanks Again

Dazza22