sql server - Conversion failed when converting date and/or time from character string. UNION CTE -

i've been given view troubleshoot. begins cte gets values of surrogate key used in several tables unions between each query. uses cte inner join select data surrogate keys. query following code:

with emp (     select distinct employeesk view1     union     select distinct employeesk table1     union     --then there 2 views if include both, overall query fails     select distinct employeesk view2     union     select distinct employeesk view3 ) select col1, col2, col3 table2 t2 inner join emp     on t2.employeesk = emp.employeesk  

whenever use cte, users error:

msg 241, level 16, state 1, line 22 conversion failed when converting date and/or time character string. 

if select each query separately returning ints. in fact, double checked each query running following query against each source:

select distinct sql_variant_property(<tablesk>, 'basetype') <source table or view> 

all queries report columns returned int.

i have created #temptable:

create table #tmp ( surrogatekey int) 

then inserted each query #temptable , inserts work. values ints. values range -1 16435.

i can queries work union long return 1 of 2 of queries. if remove either of these queries cte , union statements work, cannot use both. values these 2 queries ints , have values -1 16435 too.

i'm @ loss why error. other re-writing view stored procedure, , putting values temp table, try?