SSIS Errors

Today, while working on a new ETL in SSIS 2008 (using an old ETL as a model) I stumbled upon an error that was pretty new to me: Error at Data Flow Task [DTS.Pipeline]: input column "Column1" (1234) has lineage ID 1234 that was not previously used in the Data Flow task.

First of all, what is this lineage id? 
According to TechNet Lineage id is "a property of the component or transformation used in the data flow task. It contains an integer value that will work as buffer pointer. Each column in the data flow task will be assigned a lineage id." In fact, a column can have more than one lineage ID, if more transformations are applied on it. Basically every column has an Id pointing to the buffer.
The fix to the problem was to refresh the mapping of the columns. The mapping was not refreshed, so basically a component is waiting for something at a buffer allocation identified by something that was not used before. Reading from the position 1234 in the buffer would yield nothing since no one is writing at that position before.