Hi,
LPALST00 would be taken as default during IPL. IEFU29 is already present at SYS1.LPALIB, So try to rename the EXIT to IEEU29(SYS1.LPALIB.PLEXC or some name. Also check if you have added the SYS1.LPALIB.PLEXC at LPALST00, then you can just remove the LPA ADD statement from PROG.
add DSNAME keyword along with EXIT ADD statements.