02270. 00000 - "no matching unique or primary key for this column-list"
This:

CREATE TABLE CONFERENCESESSION (
SESSIONID CHAR(4),
BUILDINGNO CHAR(2),
ROOMNO CHAR(2),
SPEAKERID CHAR(2),
SESSIONDATE DATE,
SESSIONPRICE NUMBER(4,2),
CONSTRAINT CONFERENCESESSION_PK PRIMARY KEY(SESSIONID),
CONSTRAINT CONFERENCESESSION_FK1 FOREIGN KEY(BUILDINGNO) REFERENCES 
BUILDING(BUILDINGNO),
CONSTRAINT CONFERENCESESSION_FK2 FOREIGN KEY(ROOMNO) REFERENCES ROOM(ROOMNO),
CONSTRAINT CONFERENCESESSION_FK3 FOREIGN KEY(SPEAKERID) REFERENCES 
SPEAKER(SPEAKERID));


Should be changed to:

CREATE TABLE CONFERENCESESSION (
SESSIONID CHAR(4),
BUILDINGNO CHAR(2),
ROOMNO CHAR(2),
SPEAKERID CHAR(2),
SESSIONDATE DATE,
SESSIONPRICE NUMBER(4,2),
CONSTRAINT CONFERENCESESSION_PK PRIMARY KEY(SESSIONID),
CONSTRAINT CONFERENCESESSION_FK1 FOREIGN KEY(BUILDINGNO, ROOMNO) REFERENCES 
ROOM(BUILDINGNO, ROOMNO),
CONSTRAINT CONFERENCESESSION_FK2 FOREIGN KEY(SPEAKERID) REFERENCES 
SPEAKER(SPEAKERID));


A foreign key requires a unique or primary key constraint on the referenced columns in the parent table. A multi-column constraint is not interchangable with single-column constraints.