When in doubt, redeploy (SSRS)

Got a really persistent and "consistent" error in deployed SSRS report, which is a fairly complex one with maps: rsUnknownDataSetParameter. Just can not figure out why it complains as everything is in there. So I took the advise of a webpage and redeployed the whole report site, and whola! it works. Guess sometimes SSRS just got confused by the versions and maybe I missed something when deploy... (But I double checked!?...)