If you ever have trouble binding an xref (and who hasn’t?), the AUDIT command may help. Open the xref file, type AUDIT, and then Y to fix any errors detected. Repeat this until the command line says “Total errors found 0 fixed 0.” Then save the reference, go back to your original drawing, reload the xref, and try binding again. Proxy objects in xrefs can also be a cause of binding errors. If auditing the drawing doesn’t work, look for proxy objects with QSELECT and either explode or delete them.