No doubt somebody will run into this at some point, here it is for
reference & googleability.

The crash in mochiweb:

2012-12-06 00:06:46 =CRASH REPORT====
  crasher:
    initial call: mochiweb_acceptor:init/3
    pid: <0.11222.4523>
    registered_name: []
    exception error:
{{badmatch,{error,einval}},[{mochiweb_http,new_request,3,[{
file,"mochiweb_http.erl"},{line,129}]},{mochiweb_http,handle_invalid_request,3,[
_lib.erl"},{line,227}]}]}

The background:
In R15B02 a ddos prevention fix was applied [1],[2], that also breaks
parsing of large headers.

More info:
The thread in mochiweb [3]: will likely end up with a fix in the near
future.

[1]:
https://github.com/erlang/otp/commit/5984409d1264871cbe61bfec875de53e51713efb
[2]: http://erlang.org/pipermail/erlang-questions/2011-June/059563.html
[3]:
https://groups.google.com/forum/?fromgroups=#!topic/mochiweb/WoQMpcW8_4k

A+
Dave