Sage/ECLS internal error: No such file or directory

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It has been some time since my Sage stopped working properly. It seems symbolic computations needing libecl are broken:

sage: var('x')
x
sage: solve([x],x)

Internal or unrecoverable error in:
Got signal before environment was installed on our thread
  [2: No such file or directory]

;;; ECL C Backtrace
;;; /usr/lib64/libecl.so.13.5(si_dump_c_backtrace+0x31) [0x7f30c79e45f1]
;;; /usr/lib64/libecl.so.13.5(ecl_internal_error+0x44) [0x7f30c79cd5c4]
;;; /usr/lib64/libecl.so.13.5(+0x1b8578) [0x7f30c79fa578]
;;; /lib64/libpthread.so.0(+0xfeb0) [0x7f3105cc5eb0]
;;; /usr/lib64/libgc.so.1(+0x8bcd) [0x7f30f2130bcd]
;;; /usr/lib64/libgc.so.1(+0x68eb) [0x7f30f212e8eb]
;;; /usr/lib64/libgc.so.1(+0x6c4e) [0x7f30f212ec4e]
;;; /usr/lib64/libgc.so.1(+0x13a94) [0x7f30f213ba94]
;;; /usr/lib64/libgc.so.1(+0x87d3) [0x7f30f21307d3]
;;; /usr/lib64/libgc.so.1(+0xd659) [0x7f30f2135659]
;;; /usr/lib64/libgc.so.1(GC_generic_malloc+0x47) [0x7f30f2135757]
;;; /usr/lib64/libgc.so.1(+0xdada) [0x7f30f2135ada]
;;; /usr/lib64/libecl.so.13.5(ecl_alloc_object+0x9b) [0x7f30c7a10f7b]
;;; /usr/lib64/libecl.so.13.5(init_threads+0x42) [0x7f30c7a0e172]
;;; /usr/lib64/libecl.so.13.5(cl_boot+0x87) [0x7f30c78dd377]
;;; /usr/lib64/python2.7/site-packages/sage/libs/ecl.so(+0x6c6c) [0x7f30c7d6dc6c]
;;; /usr/lib64/python2.7/site-packages/sage/libs/ecl.so(+0x6f98) [0x7f30c7d6df98]
;;; /usr/lib64/python2.7/site-packages/sage/libs/ecl.so(initecl+0x1781) [0x7f30c7d79961]
;;; /usr/lib64/libpython2.7.so.1.0(_PyImport_LoadDynamicModule+0x99) [0x7f3105fc4a39]
;;; /usr/lib64/libpython2.7.so.1.0(+0xefc29) [0x7f3105fc2c29]
;;; /usr/lib64/libpython2.7.so.1.0(+0xefe6d) [0x7f3105fc2e6d]
;;; /usr/lib64/libpython2.7.so.1.0(PyImport_ImportModuleLevel+0x188) [0x7f3105fc37d8]
;;; /usr/lib64/libpython2.7.so.1.0(+0xd792f) [0x7f3105faa92f]
;;; /usr/lib64/libpython2.7.so.1.0(PyObject_Call+0x43) [0x7f3105f1d593]
;;; /usr/lib64/libpython2.7.so.1.0(PyEval_CallObjectWithKeywords+0x47) [0x7f3105fac477]
;;; /usr/lib64/libpython2.7.so.1.0(PyEval_EvalFrameEx+0xf05) [0x7f3105fad965]
;;; /usr/lib64/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x7dd) [0x7f3105fb251d]
;;; /usr/lib64/libpython2.7.so.1.0(PyEval_EvalCode+0x32) [0x7f3105fb2622]
;;; /usr/lib64/libpython2.7.so.1.0(PyImport_ExecCodeModuleEx+0x8c) [0x7f3105fc1d9c]
;;; /usr/lib64/libpython2.7.so.1.0(+0xef005) [0x7f3105fc2005]
;;; /usr/lib64/libpython2.7.so.1.0(+0xefc29) [0x7f3105fc2c29]
;;; /usr/lib64/libpython2.7.so.1.0(+0xefe6d) [0x7f3105fc2e6d]
Aborted

It also happens when I try to use the sum function with symbolic variables etc. The problem is not in ECLS per se, since maxima solves these things just fine.

I'm running Sage 6.5 on Gentoo Linux (using the sage-on-gentoo overlay), but the errors have been there a long time (I think < 6.2). I did various reinstalls of all my packages, also completely purged libecls, maxima, Sage and reinstalled them, but to no effect. I also tried installing all the relevant packages without threads support, as well as different versions of ECLS, nothing changed.

Does anyone have an idea what could cause this problem? Or what is even meant by the error? What file or directory isn't found?