This error may occur if you’re using sort=geodist() in your Solr Spatial / Geographic Search. The reason is probably that you have an empty pt= value or that the parameter is missing all together.
You might also want to make sure that your Solr version is new enough to support sorting by functions, but if you’re doing anything useful with spatial searches you’re probably updated enough – at least for geodist(). :-)
A question that arised at the Freenode Solr IRC channel today was about _dist_:geodist() failing to include a field named _dist_ in the response – a field which would contain the return value from geodist(), which would be the distance from the source point to the destination document. The example from the wiki is:
&q=*:*&sfield=store&pt=45.15,-93.85&sort=geodist() asc&fl=_dist_:geodist()
The _dist_:geodist() in the fl= parameter adds a field named _dist_ with the returned contents from geodist() (the :-syntax creates a field name alias).
.. but why is it missing? Probably because using geodist() in the fl parameter is only supported on Solr 4.0 and later (which is currently only in trunk).
There’s a workaround on the wiki which you can use – but this will not allow you to score documents in any other way – the score returned will be the value of geodist() by using geodist() as the query:
q={!func}geodist()