ETL Load issue from char to bigint

Database

ETL Load issue from char to bigint

I am trying to populate a column in a table which has data type as a bigint.
Inspite of converting the incoming data from string to bigint I am getting the following error.

UTY8001 RDBMS failure in Stmt Check: 3754, Precision error in FLOAT type
constant or during implicit conversions.

When I changed the datatype of target column to varchar (20) it worked fine.

I will appreciate if someone has experience of dealing with a similar issue and if you can share that with us.