I'm also having this same problem when I click "attach to project."
The package version is 6.10.58+dfsg-3 and I'm using Maverick.

I doubt this helps much but this is the output of "boincmgr" with no options, up to the button press
:
10:05:14 PM: Error: Memory VFS already contains file 'webexternallink.xpm'!
10:05:14 PM: Error: Memory VFS already contains file 'nvidiaicon.xpm'!
10:05:14 PM: Error: Memory VFS already contains file 'atiicon.xpm'!
10:05:14 PM: Error: Memory VFS already contains file 'multicore.xpm'!
SIGSEGV: segmentation violation
Stack trace (58 frames):
boincmgr(boinc_catch_signal+0x4d)[0x523d0d]
/lib/libpthread.so.0(+0xfb40)[0x7f9770420b40]
boincmgr[0x4a54ea]
boincmgr[0x4a4056]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler21ProcessEventIfMatchesERK21wxEventTableEntryBasePS_R7wxEvent+0x50)[0x7f97709a6310]
/usr/lib/libwx_baseu-2.8.so.0(_ZN16wxEventHashTable11HandleEventER7wxEventP12wxEvtHandler+0xa4)[0x7f97709a72d4]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler12ProcessEventER7wxEvent+0xc7)[0x7f97709a73b7]
boincmgr[0x521af3]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler21ProcessEventIfMatchesERK21wxEventTableEntryBasePS_R7wxEvent+0x50)[0x7f97709a6310]
/usr/lib/libwx_baseu-2.8.so.0(_ZN16wxEventHashTable11HandleEventER7wxEventP12wxEvtHandler+0xa4)[0x7f97709a72d4]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler12ProcessEventER7wxEvent+0xc7)[0x7f97709a73b7]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN12wxWindowBase9TryParentER7wxEvent+0x39)[0x7f9771116209]
/usr/lib/libwx_gtk2u_core-2.8.so.0(+0x216639)[0x7f9771058639]
/usr/lib/libgobject-2.0.so.0(g_closure_invoke+0x15e)[0x7f976dd70a6e]
/usr/lib/libgobject-2.0.so.0(+0x248d4)[0x7f976dd868d4]
/usr/lib/libgobject-2.0.so.0(g_signal_emit_valist+0x7e6)[0x7f976dd87996]
/usr/lib/libgobject-2.0.so.0(g_signal_emit+0x83)[0x7f976dd87f53]
/usr/lib/libgtk-x11-2.0.so.0(+0x8de85)[0x7f976f35ee85]
/usr/lib/libgobject-2.0.so.0(g_closure_invoke+0x15e)[0x7f976dd70a6e]
/usr/lib/libgobject-2.0.so.0(+0x23da1)[0x7f976dd85da1]
/usr/lib/libgobject-2.0.so.0(g_signal_emit_valist+0x7e6)[0x7f976dd87996]
/usr/lib/libgobject-2.0.so.0(g_signal_emit+0x83)[0x7f976dd87f53]
/usr/lib/libgtk-x11-2.0.so.0(+0x8cb8d)[0x7f976f35db8d]
/usr/lib/libgtk-x11-2.0.so.0(+0x13a9d8)[0x7f976f40b9d8]
/usr/lib/libgobject-2.0.so.0(g_closure_invoke+0x15e)[0x7f976dd70a6e]
/usr/lib/libgobject-2.0.so.0(+0x24120)[0x7f976dd86120]
/usr/lib/libgobject-2.0.so.0(g_signal_emit_valist+0x62b)[0x7f976dd877db]
/usr/lib/libgobject-2.0.so.0(g_signal_emit+0x83)[0x7f976dd87f53]
/usr/lib/libgtk-x11-2.0.so.0(+0x2536df)[0x7f976f5246df]
/usr/lib/libgtk-x11-2.0.so.0(gtk_propagate_event+0xc3)[0x7f976f403e73]
/usr/lib/libgtk-x11-2.0.so.0(gtk_main_do_event+0x2eb)[0x7f976f404f4b]
/usr/lib/libgdk-x11-2.0.so.0(+0x5c74c)[0x7f976f07e74c]
/lib/libglib-2.0.so.0(g_main_context_dispatch+0x1f2)[0x7f976d4af342]
/lib/libglib-2.0.so.0(+0x442a8)[0x7f976d4b32a8]
/lib/libglib-2.0.so.0(g_main_loop_run+0x195)[0x7f976d4b37b5]
/usr/lib/libgtk-x11-2.0.so.0(gtk_main+0xa7)[0x7f976f4053e7]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN11wxEventLoop3RunEv+0x48)[0x7f9771012578]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN8wxDialog9ShowModalEv+0xb3)[0x7f9771063dd3]
boincmgr[0x521f88]
boincmgr[0x51cffc]
boincmgr[0x4b2e47]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler21ProcessEventIfMatchesERK21wxEventTableEntryBasePS_R7wxEvent+0x50)[0x7f97709a6310]
/usr/lib/libwx_baseu-2.8.so.0(_ZN16wxEventHashTable11HandleEventER7wxEventP12wxEvtHandler+0xa4)[0x7f97709a72d4]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler12ProcessEventER7wxEvent+0xc7)[0x7f97709a73b7]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxEvtHandler20ProcessPendingEventsEv+0x60)[0x7f97709a6760]
/usr/lib/libwx_baseu-2.8.so.0(_ZN12wxAppConsole20ProcessPendingEventsEv+0x49)[0x7f9770918299]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN9wxAppBase11ProcessIdleEv+0x1b)[0x7f9771097c7b]
/usr/lib/libwx_gtk2u_core-2.8.so.0(+0x1b95d0)[0x7f9770ffb5d0]
/lib/libglib-2.0.so.0(g_main_context_dispatch+0x1f2)[0x7f976d4af342]
/lib/libglib-2.0.so.0(+0x442a8)[0x7f976d4b32a8]
/lib/libglib-2.0.so.0(g_main_loop_run+0x195)[0x7f976d4b37b5]
/usr/lib/libgtk-x11-2.0.so.0(gtk_main+0xa7)[0x7f976f4053e7]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN11wxEventLoop3RunEv+0x48)[0x7f9771012578]
/usr/lib/libwx_gtk2u_core-2.8.so.0(_ZN9wxAppBase8MainLoopEv+0x4b)[0x7f9771097b0b]
/usr/lib/libwx_baseu-2.8.so.0(_Z7wxEntryRiPPw+0x85)[0x7f977094c695]
boincmgr[0x44a6f2]
/lib/libc.so.6(__libc_start_main+0xfe)[0x7f976f90dd8e]
boincmgr[0x4211a9]

Exiting...