Hello, I've compiled LyX 5.0 svn.
1) Open User Guide 2) Tools -> outline 3) Document -> Next cross-reference 4) Click in the Toc Widget on the second section 5) Boum with this (rather unhelpful message) /usr/include/c++/4.1.3/debug/safe_iterator.h:130:error: attempt to copy- construct an iterator from a singular iterator. Objects involved in the operation: iterator "this" @ 0x0xaf918fe0 { type = N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPKN3lyx7TocItemEN10__gnu_norm6vectorIS4_SaIS4_EEEEEN15__gnu_debug_def6vectorIS4_S9_EEEE (constant iterator); state = singular; } iterator "other" @ 0x0x92abed0 { type = N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPKN3lyx7TocItemEN10__gnu_norm6vectorIS4_SaIS4_EEEEEN15__gnu_debug_def6vectorIS4_S9_EEEE (constant iterator); state = singular; } Cheers, Charles