How do we try to know if it is a regression curve or a smoothed curve? GOG_IS_REG_CURVE would tell if it is a regression curve. GOG_IS_SMOOTHED_CURVE is the other possible test.

Let's worry about the first warning. We have in openoffice-write.c:
------------------------------------------------------------------
GSList *l, *regressions = gog_object_get_children
		(series, role);
char *str;

for (l = regressions; l != NULL && l->data != NULL; l = l->next) {
	GOData const *bd;
	GogObject const *regression = l->data;
	GogObject const *equation
		= gog_object_get_child_by_name (regression, "Equation");
...
if (equation != NULL) {
		GObjectClass *klass = G_OBJECT_GET_CLASS (equation);
...
------------------------------------------------------------------

The "(gnumeric:25987): GLib-CRITICAL **: g_hash_table_lookup: assertion `hash_table != NULL' failed" is triggered by the gog_object_get_child_by_name. We ar elater checking whether equation is null, unfortunately we get the critical rather than just a NULL.

The second critical appears in the same code snippet:
--------------------------------------------------------------
GSList *l, *regressions = gog_object_get_children
	(series, role);
char *str;

for (l = regressions; l != NULL && l->data != NULL; l = l->next) {
	GOData const *bd;
	GogObject const *regression = l->data;
	GogObject const *equation
		= gog_object_get_child_by_name (regression, "Equation");

	str = odf_get_gog_style_name_from_obj
		(GOG_OBJECT (regression));
	gsf_xml_out_start_element
		(state->xml,
		 (l == regressions) ? CHART "regression-curve"
		 : GNMSTYLE "regression-curve");
	gsf_xml_out_add_cstr (state->xml, CHART "style-name", str);

	if (state->with_extension) {
		/* Upper and lower bounds */
		bd = gog_dataset_get_dim (GOG_DATASET (regression), 0);
		if (bd != NULL)
...

--------------------------------------------------------------

It is triggered by the 
gog_dataset_get_dim (GOG_DATASET (regression), 0);

again a straight NULL would be preferable.

For the last comment, you should never call gog_dataset_get_dim () if you don't know which are the correct indices (this is a feature).
gog_dataset_dims() tells which are the first and last that you can use.

Created attachment 195753 [details] [review]
Proposed patch

Please, test with this patch.

Review of attachment 195753 [details] [review]:

please commit

This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.