Problem with at_askml function in Postgis

Using PostgreSQL 9.1.8 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit
POSTGIS="2.0.1 r9979" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.9.2, released 2012/10/08" LIBXML="2.8.0" LIBJSON="UNKNOWN" TOPOLOGY RASTER

Postgis seems to be working fine, but when I try this query
SELECT st_askml(path) FROM paths WHERE jobnumber = '20121491';

I get this error
ERROR: function st_askml(geometry) is not unique
LINE 1: select st_askml(path) from paths where jobnumber = '20121491...
^
HINT: Could not choose a best candidate function. You might need to add explicit type casts.

If I change the query to
SELECT st_askml(path,15) FROM paths WHERE jobnumber = '20121491';

Then it works

Both st_askml(geometry) and st_askml(geometry, integer) are unique.

Does anybody know the answer to this problem?