Gentoo installer is crashing in some situtation, and this is error report for user. End user need to read logs for reason of this CRASH. Installer should report problems in more friendly way. Error is related to error report about unkown partition (Bug#: 146600)
Erm, installer already told you nicely that your partitions are not recognized. You chose to completely ignore that nice message, so it crashed on you instead of nuking your data. It's intentional, as already told you on the other bug. *** This bug has been marked as a duplicate of 146600 ***