Hi,
FlexCelImport and FlexCelAdapter are units from FlexCel 3, they don't exist anymore in FlexCel 6. You can still use them by installing the latest FlexCel 3 after installing FlexCel 6 (FlexCel 3 is on our registered users page below FlexCel 6), and changing your TXlsAdapters by TXlsxAdapters. This way you can keep the old code running, but supporting xlsx, recalculation, and all the new stuff in FlexCel 6. Or you can migrate the code, it isn't really hard (TFlexCelImport is now named TXlsFile and it not a component anymore, but the methods are very similar)
You can find more information here:
http://www.tmssoftware.biz/flexcel/docs/vcl/MigratingFromFlexCel3.pdf