Use XS++ v3.1 and flash only Main and FS!

XS++ 3.1 Guide-Flashing, Customizing, Recovering - Top Sony Forums

If you haven't installed USB flash driver read here: USB Flash Driver Installation - Guide - Top Sony Forums

Downloads - R4CB020_RED49 - Top Sony Forums

Etc.

W550_R4CB020_FS_EMEA_3_RED49
W550_CDA102426_3_R2A_Generic_EMEA_3
W550_R4CB020_MAIN_GENERIC_EL_RED49

or

W550_R4CB020_FS_EUROPE_4_RED49
HB1-06_Gen_CDA102568_13_R8A_GENERIC_EUROPE_4
W550_R4CB020_MAIN_GENERIC_EL_RED49

Custom file you must flash with Setool: SeTool2 Lite 1.11 - Top Sony Forums
Downloads - w550custpack - Top Sony Forums