Ivan,yes, I've changed the structure of one table on SSMS (alter columns from integer to decimal), and wanted to check if I could do it with DDT. So I've done the same changes in DDT project.
Trent,
the error occurs on building the package, not on deployment. But having a look in my project, I can see that the indexes with more than 16 columns included have been imported. As we know now that there is a problem here, that index is probably the culprit. I'll have a try without this index.