Index: trunk/src_plugins/export_openems/export_openems.c
===================================================================
--- trunk/src_plugins/export_openems/export_openems.c	(revision 32006)
+++ trunk/src_plugins/export_openems/export_openems.c	(revision 32007)
@@ -639,7 +639,8 @@
 		openems_wr_m_testpoints(&wctx, wctx.pcb->Data);
 	}
 	else { /* xml */
-		openems_wr_xml(&wctx);
+		if (openems_wr_xml(&wctx) != 0)
+			rnd_message(RND_MSG_ERROR, "openEMS: Due to errors, the exported file is invalid.\n");
 	}
 
 	rnd_conf_update(NULL, -1); /* restore forced sets */
@@ -719,7 +720,8 @@
 	if (flags & PCB_LYT_COPPER) { /* export copper layers only */
 		ems_ctx->clayer = ems_ctx->lg_pcb2ems[group];
 		if ((!ems_ctx->fmt_matlab) && (!is_empty))
-			openems_wr_xml_layergrp_begin(ems_ctx, &ems_ctx->pcb->LayerGroups.grp[group]);
+			if (openems_wr_xml_layergrp_begin(ems_ctx, &ems_ctx->pcb->LayerGroups.grp[group]) != 0)
+				return 0;
 		return 1;
 	}
 	return 0;
Index: trunk/src_plugins/export_openems/openems_xml.c
===================================================================
--- trunk/src_plugins/export_openems/openems_xml.c	(revision 32006)
+++ trunk/src_plugins/export_openems/openems_xml.c	(revision 32007)
@@ -55,7 +55,7 @@
 	return pcb_stack_thickness(ctx->pcb, "openems", PCB_BRDTHICK_PRINT_ERROR, from, 1, to, 0, PCB_LYT_SUBSTRATE|PCB_LYT_COPPER);
 }
 
-static void openems_wr_xml_layergrp_begin(wctx_t *ctx, pcb_layergrp_t *g)
+static int openems_wr_xml_layergrp_begin(wctx_t *ctx, pcb_layergrp_t *g)
 {
 	rnd_coord_t th;
 	pcb_layer_t *ly = NULL;
@@ -80,8 +80,10 @@
 	fprintf(ctx->f, "        <Primitives>\n");
 	ctx->cond_sheet_open = 1;
 	th = get_grp_elev(ctx, g);
-TODO("check for -1 and return error");
+	if (th < 0)
+		return -1;
 	ctx->elevation = RND_COORD_TO_MM(th);
+	return 0;
 }
 
 static int openems_wr_xml_outline(wctx_t *ctx, pcb_layergrp_t *g)
@@ -124,10 +126,12 @@
 }
 
 
-static void openems_wr_xml_grp_substrate(wctx_t *ctx, pcb_layergrp_t *g)
+static int openems_wr_xml_grp_substrate(wctx_t *ctx, pcb_layergrp_t *g)
 {
 	rnd_coord_t th = get_grp_elev(ctx, g);
-TODO("check for -1 and return error");
+
+	if (th < 0)
+		return -1;
 	ctx->elevation = RND_COORD_TO_MM(th);
 
 TODO("Fix hardwired constants");
@@ -139,12 +143,14 @@
 	openems_wr_xml_outline(ctx, g);
 	fprintf(ctx->f, "        </Primitives>\n");
 	fprintf(ctx->f, "      </Material>\n");
+	return 0;
 }
 
-static void openems_wr_xml_layers(wctx_t *ctx)
+static int openems_wr_xml_layers(wctx_t *ctx)
 {
 	rnd_hid_expose_ctx_t ectx = {0};
 	rnd_cardinal_t gid;
+	int err = 0;
 
 	fprintf(ctx->f, "    <Properties>\n");
 
@@ -160,11 +166,12 @@
 	for(gid = 0; gid < ctx->pcb->LayerGroups.len; gid++) {
 		pcb_layergrp_t *g = &ctx->pcb->LayerGroups.grp[gid];
 		if (g->ltype & PCB_LYT_SUBSTRATE)
-			openems_wr_xml_grp_substrate(ctx, g);
+			err |= openems_wr_xml_grp_substrate(ctx, g);
 	}
 
 
 	fprintf(ctx->f, "    </Properties>\n");
+	return err;
 }
 
 static void openems_wr_xml_mesh_lines(wctx_t *ctx, pcb_mesh_t *mesh, char axis, pcb_mesh_lines_t *l, rnd_coord_t scale)
@@ -187,12 +194,12 @@
 	fprintf(ctx->f, "    </RectilinearGrid>\n");
 }
 
-static void openems_wr_xml(wctx_t *ctx)
+static int openems_wr_xml(wctx_t *ctx)
 {
 	pcb_mesh_t *mesh = pcb_mesh_get(MESH_NAME);
 	char *exc;
+	int err = 0;
 
-
 	fprintf(ctx->f, "<?xml version='1.0' encoding='UTF-8' standalone='yes' ?>\n");
 	fprintf(ctx->f, "<openEMS>\n");
 	fprintf(ctx->f, "  <FDTD NumberOfTimesteps='%ld' endCriteria='%f' f_max='%ld'>\n", def_num_timesteps, def_end_crit, def_f_max);
@@ -217,11 +224,12 @@
 	fprintf(ctx->f, "  <ContinuousStructure CoordSystem='0'>\n");
 	fprintf(ctx->f, "    <BackgroundMaterial Epsilon='%f' Mue='%f' Kappa='0' Sigma='0'/>\n", ctx->options[HA_void_epsilon].dbl, ctx->options[HA_void_mue].dbl);
 
-	openems_wr_xml_layers(ctx);
+	err |= openems_wr_xml_layers(ctx);
 	openems_wr_xml_grid(ctx, mesh);
 	fprintf(ctx->f, "  </ContinuousStructure>\n");
 
 
 	fprintf(ctx->f, "</openEMS>\n");
+	return err;
 }