yaml export error

[jihoonl]

# client
jihoonl@whoola:~$ rosservice call /software/world_canvas/yaml_export tt
result: False
message: Export to file failed: unpack requires a string argument of length 4

# server
[ERROR] [WallTime: 1412779323.836985] Export to file failed: unpack requires a string argument of length 4

[corot]

Cannot reproduce it