Unhelpful metapost error

[Olly Betts]

My, I'm all questions today...

When I try to process my survey to produce a PDF plan, metapost appears
to not like something, but there's no error message, so I've no idea
where to look.

I've attached the log, I can send other stuff if that's helpful.

This is therion 0.3.3 on Linux, with THUSESVX defined.

Cheers,
    Olly



therion 0.3.3
initialization file: /etc/therion.ini
reading ... done
configuration file: thconfig
reading ... done
reading source files ... done
preprocessing database ... done
processing survey data ...
####################### cavern log file ########################
 1> Survex 1.0.31
 2> Copyright (C) 1990-2004 Olly Betts
 3> Survey has no fixed points. Therefore I've fixed 1 at (0,0,0)
 4>
 5> Survey contains 275 survey stations, joined by 274 legs.
 6> There are 0 loops.
 7> Total length of survey legs = 1180.04m (1180.04m adjusted)
 8> Total plan length of survey legs =  868.99m
 9> Total vertical length of survey legs =  522.64m
10> Vertical range = 189.70m (from 21 at 2.59m to 185 at -187.11m)
11> North-South range = 139.82m (from 261 at 16.42m to 242 at -123.40m)
12> East-West range = 145.01m (from 196 at 34.11m to 231 at -110.90m)
13>   32 1-nodes.
14>  219 2-nodes.
15>   19 3-nodes.
16>    4 4-nodes.
17>    1 5-node.
18>
######################### transcription ########################
 3> 1 : 2 at entrance.76
 5> 275 : 15 at boiling.76 -- 274 : 14 at boiling.76
10> 21 : 1 at bent.76 -- 185 : 11 at keg.76
11> 261 : 1 at boiling.76 -- 242 : 12 at noways.76
12> 196 : 3 at tap.76 -- 231 : 1 at noways.76
13> 32 : 5 at brave.76
14> 219 : 5 at rift.76
15> 19 : 8 at bent.76
16> 4 : 4 at entrance.76
17> 1 : 2 at entrance.76
#################### end of cavern log file ####################
done
calculating basic statistics ... done
processing references ... done
selecting export objects ... done
scanning centreline tree ... done
processing projection plan ... done
average distortion: 2.77%
writing 76_plan.pdf ...
####################### metapost log file ########################
Survex 1.0.31
Copyright (C) 1990-2004 Olly Betts
Survey has no fixed points. Therefore I've fixed 1 at (0,0,0)

Survey contains 275 survey stations, joined by 274 legs.
There are 0 loops.
Total length of survey legs = 1180.04m (1180.04m adjusted)
Total plan length of survey legs =  868.99m
Total vertical length of survey legs =  522.64m
Vertical range = 189.70m (from 21 at 2.59m to 185 at -187.11m)
North-South range = 139.82m (from 261 at 16.42m to 242 at -123.40m)
East-West range = 145.01m (from 196 at 34.11m to 231 at -110.90m)
  32 1-nodes.
 219 2-nodes.
  19 3-nodes.
   4 4-nodes.
   1 5-node.

#################### end of metapost log file ####################
therion: error -- metapost exit code -- 256