Specific user cannot login anymore: error code='503'

Hi,

all of a sudden user user@domain.com (Adium on a Mac) cannot login anymore. Debug-output looks like this:

D(<0.400.0>:ejabberd_c2s:1553) : Send XML on stream = <<"">>

And a few lines later:

"(ejabberd@service) The process <0.5.0> is consuming too much memory:\n[{old_heap_block_size,1346269},\n {heap_block_size,196418},\n {mbuf_size,0},\n {stack_size,172},\n {old_heap_size,374847},\n {heap_size,2625}]\n[{current_function,{io,wait_io_mon_reply,2}},\n {initial_call,{proc_lib,init_p,5}},\n {message_queue_len,3},\n {links,[<0.0.0>,<0.29.0>,#Port<0.3406>]},\n {dictionary,[{'$ancestors',[<0.2.0>]},\n {'$initial_call',{gen_event,init_it,6}}]},\n {heap_size,196418},\n {stack_size,35}]"}]}]}

ejabberd is on a Ubuntu 12.04 Machine.

Same user user@domain.com on an Android can log in (with xabber).

What could be the reason for that? Thanks in advance!