Thanks JMH for pointing me in the right direction.
I'm using a variable 'NOER' within a binary data file to set rigid bed level, and I had accidentally left the code looking in T2D_FILES(T2DBI1), instead of T3D equivalents.
Strangely, changing to T3D_FILES(T3DBI1) fixed the first error, but instead gives 'NEGATIVE DEPTH PRESCRIBED ON BOUNDARY' error.
I found it worked fine if I copied the NOER variable into the geometry file, and used T3D_FILES(T3DGEO) as I had on earlier initial runs..
e.g.
CALL BIEF_ALLVEC(1,NOER,'NOER ',IELMT,1,2,MESH)
ALLOCATE(W(NPOIN),STAT=ERR)
NAME='NOER '
CALL FIND_IN_SEL(NOER,NAME,T3D_FILES(T3DGEO)%LU,
& W,OK)
CALL OV( 'X=Y+C ',ZR,NOER%R,ZF,0.D0,NPOIN)
Weird, because including NOER in a separate binary file (which I thought was 'cleaner') works fine in Telemac2D runs...
Anyway, problem solved
Thanks,
Dougal