This Database level I/O Error Occurred (-51)error appears in sde.errlog when trying to display a registered SDO layer:
SE_DB_IO_ERROR: Invalid grid size error (-33)
This error can occur when attempting to display, query, or zoom an Oracle Spatial feature class via ESRI applications such as ArcCatalog, ArcMap, ArcView, MapObjects or ArcIMS.
SDO_LEVEL is set too small.
Increase SDO_LEVEL parameter in the DBTUNE table.
See Oracle documentation for an explanation of the SDO_LEVEL parameter.