java.lang.ClassCastException because of "WHERE" condition in Query Dialog??

Hello,

after modifying my SQL Query inside the query dialog I, all of a sudden, got this error message when previewing my report:

java.lang.ClassCastException: java.math.BigDecimal cannot be cast to java.lang.String

Here is the query: (very simple one!)

select top 200001 "ProjectType"."ProjectType" as "ProjectType",

"hours_costs"."period_type" as "period_type"

from blablabla

where "INVESTMENTS"."OBJECT_CODE" = 'project' and "mapping_v"."level3" like 'R&D%%' and "mapping_v"."type_id" = 'depts'

and "hours_costs"."period_type" like '%Actual Year%' <------ Removing this line allow the report to run!!!! why?!?!? is this a bug??? group by "ProjectType"."ProjectType" order by "ProjectType"."ProjectType"

Is there a known bug and/or workaround for this??? Thanks in advance for any help :)