SQL Server Conversion failed when converting datetime from character string -

i have query fill in date in table that's giving me error message:

conversion failed when converting datetime character string.

below table declaration , query. doing wrong , how can fix it?

create table #inv (       rep_lname nvarchar(50)     , rep_fname nvarchar(50)     , rep_id nvarchar(50)     , rep_email nvarchar(100)     , rep_status nvarchar(50)     , rep_bu nvarchar(50)     , sales_force nvarchar(50)     , territory nvarchar(50)     , sample_eligibility nvarchar(50)     , dm_name nvarchar(100)     , phys_inv_date datetime     , last_reconciled datetime     , inv_type nvarchar(50)     , days_since_last_inv int ) 

i'm trying fill phys_inv_date field inside cursor so:

open inventory_info  fetch next inventory_info @rep_id, @call_date  while ( @@fetch_status = 0 ) begin            select             @ls_sql = 'update #inv set phys_inv_date = case when inventory_type = ''physical'' '             + @call_date             + ' else b.inv_date end #inv inner join (select top 1 call_date, rep_id inv_header call_date < '             + @call_date + ' , rep_id = ''' + @rep_id             + ''') b on a.rep_id = b.rep_id phys_inv_date null'          exec (@ls_sql)          fetch next inventory_info @rep_id, @call_date  end  close inventory_info deallocate inventory_info 

what's wrong using sql parameters? there's no obvious reason why need dynamic sql here, , assuming variables correct data types won't need convert anything:

update      #inv  set      phys_inv_date = case          when inventory_type = 'physical' @call_date         else b.inv_date end       #inv      inner join (         select top 1              call_date,              rep_id                       inv_header call_date < @call_date             , rep_id = @rep_id     ) b     on a.rep_id = b.rep_id       phys_inv_date null