Task fails on server but not on my development PC

hi

I have this annoying error on my server but not in my PC,

When I run the task from VisualStudio2010 it works perfectly. Then I deploy the package to my SqlServer2012 "Intgegration Services Catalogs" and run the deployed package from the SqlManagementConsole I got the error.

The source is an oracle DB and the query wich calculate the field "MONJTO_HRSEXTR" do it with this "sum(nvl(h.monto,0)) monto_hrsext" on the select statement.

I guess the problem is SSIS thinks that the column MONTO_HRSEXTR is "Unicode string[DT_WSTR]" with "lenght=38" and when the conversion process try to cast to Decimal(12,2) it fails. There are 2 big questions here

1.Why it works on my development PC and not in the server when deployed?

2.why the "Data Conversion Transtormation Editor" thinks the field is a  Unicode string[DT_WSTR] if that field is a sum result from numerics fields in the oracle table

Thanks a lot!!! for any Idea

Salu2 Sergio T