I don't know why, but Ms Access has some problem with operator in my statement:/
Code:
Dim strSQL As String
strSQL = "Update TblRozklad set [ProcentZcalosci] = ([Naklad] * 100 / Sum([Naklad].tblRozklad) * Forms!frmRozkladGlowny!IloscUzytkow / 100) GROUP BY ([Naklad] * 100 / Sum([Naklad].TblRozklad) * Forms!frmRozkladGlowny!IloscUzytkow / 100)"
CurrentDb.Execute (strSQL), dbFailOnError