--- grass57dataset.cpp.orig	2006-11-09 16:05:39.000000000 +0100
+++ grass57dataset.cpp	2006-11-09 16:54:19.000000000 +0100
@@ -1,5 +1,5 @@
 /******************************************************************************
- * $Id: grass57dataset.cpp,v 1.6 2006/02/13 17:39:31 rblazek Exp $
+ * $Id: grass57dataset.cpp,v 1.7 2006/11/09 15:30:45 rblazek Exp $
  *
  * Project:  GRASS Driver
  * Purpose:  Implement GRASS raster read/write support
@@ -31,6 +31,9 @@
  ******************************************************************************
  *
  * $Log: grass57dataset.cpp,v $
+ * Revision 1.7  2006/11/09 15:30:45  rblazek
+ * check if ResetReading failed
+ *
  * Revision 1.6  2006/02/13 17:39:31  rblazek
  * header files moved to grass
  *
@@ -73,7 +76,7 @@
 
 #define GRASS_MAX_COLORS 100000  // what is the right value
 
-CPL_CVSID("$Id: grass57dataset.cpp,v 1.6 2006/02/13 17:39:31 rblazek Exp $");
+CPL_CVSID("$Id: grass57dataset.cpp,v 1.7 2006/11/09 15:30:45 rblazek Exp $");
 
 CPL_C_START
 void	GDALRegister_GRASS(void);
@@ -409,7 +412,10 @@
 	 sNewWindow->ew_res != sOpenWindow.ew_res || sNewWindow->ns_res != sOpenWindow.ns_res ||
 	 sNewWindow->rows   != sOpenWindow.rows   || sNewWindow->cols   != sOpenWindow.cols )
     {
-        G_close_cell( hCell );
+	if( hCell >= 0 ) {
+            G_close_cell( hCell );
+	    hCell = -1;
+	}
 
 	/* Set window */
 	G_set_window( sNewWindow );
@@ -423,6 +429,7 @@
 	
 	if ( (hCell = G_open_cell_old( pszCellName, pszMapset)) < 0 ) {
 	    CPLError( CE_Warning, CPLE_AppDefined, "GRASS: Cannot open raster '%s'", pszCellName );
+            this->valid = false;
 	    return CE_Failure;
 	}
 
@@ -459,6 +466,8 @@
 CPLErr GRASSRasterBand::IReadBlock( int nBlockXOff, int nBlockYOff, void * pImage )
 
 {
+    if ( ! this->valid ) return CE_Failure;
+
     // Reset window because IRasterIO could be previosly called
     if ( ResetReading ( &(((GRASSDataset *)poDS)->sCellInfo) ) != CE_None ) {
        return CE_Failure;
@@ -510,6 +519,8 @@
     /* Calculate the region */
     struct Cell_head sWindow;
     struct Cell_head *psDsWindow;
+    
+    if ( ! this->valid ) return CE_Failure;
 
     psDsWindow = &(((GRASSDataset *)poDS)->sCellInfo);
     
@@ -526,7 +537,10 @@
     /* Reset resolution */
     G_adjust_Cell_head ( &sWindow, 1, 1);
 
-    ResetReading ( &sWindow );
+    if ( ResetReading ( &sWindow ) != CE_None )
+    {
+        return CE_Failure;
+    }
     
     /* Read Data */
     CELL  *cbuf = NULL;