Index: trunk/psastro/src/psastroUtils.c
===================================================================
--- trunk/psastro/src/psastroUtils.c	(revision 41895)
+++ trunk/psastro/src/psastroUtils.c	(revision 42289)
@@ -109,8 +109,18 @@
 
     psRegion *region = pmChipPixels (chip);
-
     psFree (chip->fromFPA);
     chip->fromFPA = psPlaneTransformInvert (NULL, chip->toFPA, *region, 50, 4);
     psFree (region);
+
+    // XXX EAM 2022.09.22 : for a specific case, psPlaneTransformInvert fails.
+    // This probably means the solution was poor in any case.  
+    // Some options:
+    // 1) skip the chip in psastroAstromGuessCheck (supply bad corners)
+    // 2) mark this chip as bad (return an error here and trap in psastroMosaicOneChip)
+    // 3) warn of the failure:
+    if (!chip->fromFPA) {
+	char *name = psMetadataLookupStr (NULL, chip->concepts, "CHIP.NAME");
+	psLogMsg ("psastro", PS_LOG_INFO, "WARNING: failure to invert toFPA for %s", name);
+    }
 
     // loop over cells in this chip
@@ -150,4 +160,5 @@
 		    pmAstromObj *ref = refstars->data[i];
 		    psPlaneTransformApply (ref->chip, chip->fromFPA, ref->FP);
+		    // if chip->fromFPA is NULL (non-invertable), the action is skipped
 		}
 	    }