SQL - Conversion of char to datetime data type error

[darbid]

I could never write a query like this, I am getting help from someone with sql experience but zero Access/Sql experience

Could someone please help us with this error message

Full out join

Error - the conversion of a char data type to a datetime data type resulted in an out of range datetime value #242​

We are using the below query as a passthrough query

Full out join[FONT=Arial][COLOR=#0000ff][SIZE=2]select project.yemo , contactcount,  projectcount
From
(SELECT year(Date_of_Contact) + month(Date_of_Contact) AS yemo, count(Date_of_Contact) as  contactcount
From [tbl_LuT Vorgang]
WHERE  [tbl_LuT  Vorgang].Date_of_Contact >= '01/10/2008' AND [tbl_LuT  Vorgang].Date_of_Contact <= '30/03/2009'
GROUP by  year(Date_of_Contact) +  month(Date_of_Contact) )  contact
full Outer join
(SELECT  year(Date_of_Project) +  month(Date_of_Project) AS yemo,  count (Date_of_Project) as projectcount
From [tbl_LuT Vorgang]
WHERE  [tbl_LuT Vorgang].Date_of_Project >= '01/10/2008'  AND [tbl_LuT  Vorgang].Date_of_Project <='30/03/2009'
GROUP by  year(Date_of_Project) +  month(Date_of_Project) ) project [/SIZE][/COLOR][/FONT]
 [FONT=Arial][COLOR=#0000ff][SIZE=2]ON isnull(contact.yemo,'XZ1ZX') = isnull(project.yemo,'XZ1ZX');  [/SIZE][/COLOR][/FONT]