(ROWLOCK) VS (HOLDLOCK, UPDLOCK)

i have a project server select thats selecting a single record. the holdlock ,updlock is locking up. If i change it to rowlock it runs fine. Can someone explain the difference between (ROWLOCK) VS (HOLDLOCK, UPDLOCK)declare @proj_uid uniqueidentifier, @res_uid uniqueidentifier, @assn_uid uniqueidentifierSET @proj_uid='11111111-1111-1111-1111-111111111111'SET @res_uid='0C8832DD-3681-4238-A4DA-5342308DDBED' SELECT @assn_uid = ASSN_UID FROM dbo.MSP_ASSN_ENTERPRISE with (HOLDLOCK, UPDLOCK) WHERE PROJ_UID = @proj_uid AND RES_UID = @res_uid