Trying to add the postgis extension to postgresql but getting the error;
ERROR: could not load library "/usr/lib/postgresql/9.1/lib/postgis-2.1.so": /usr/lib/postgresql/9.1/lib/postgis-2.1.so: undefined symbol: GEOSRelatePatternMatch
Any suggestions as to what this means? I can't access the .so to have a look but the file is there in the direcoty specified in the error.
Environment is Ubuntu 12.4