Understanding Society User Support

Greetings,

I'm trying to use the BHPS armonised files, and wanted to merge files in the same waves (I need to merge indresp, income and jobhist). The problem is that the pid and pidp variables, that are suppose to uniquely identify each individual, do not actually do it. What I mean is, each individual, identified through the pid or pidp variables, appears in multiple rows, so when I try to merge the files I get the error saying that "variable pidp(or pid) does not uniquely identify observations in the using data".
Any help on the matter would be really appreciated!