I'm trying to configure a custom grid in mapproxy but almost every configuration I've tested results in a 500 Internal Server Error with no information in the log when requesting a GetCapabilities response. I'll post the complete config below, but this is the problem section:
custom_grid is referenced by a cache whose source is a WMS service that does support EPSG:4269. I've tried using a range of EPSG codes taken from the upstream WMS's SRS list and they all fail in the same way. While testing this issue I only have a single layer, source, cache, and grid.
If I set the grid srs property to EPSG:4326, EPSG:3857, EPSG:900913, or EPSG:102100 I get the expected GetCapabilities document. Anything other than these somewhat standard values throws the error. I have tried removing and changing the 'base' property but this made no difference.
In trying to understand the issue I reviewed the mapproxy source and saw that by setting MAPPROXY_USE_PYPROJ and installing pyproj (using version 1.9.6 thanks to this issue) I can use pyproj instead of libproj. However this also made no difference.
Can anyone tell me what might be causing the error when an uncommon srs property is used in the grid and how I might address it? Any help much appreciated!