From downstream report: 

https://bugzilla.redhat.com/show_bug.cgi?id=670522

xfce4-settings is crashing on login. 

Start of backtrace (full trace available at above bug): 

Core was generated by `xfce4-settings-helper'.
Program terminated with signal 6, Aborted.
#0  0x00007f822fab41b5 in raise () from /lib64/libc-2.12.90.so

Thread 1 (Thread 0x7f82326d29a0 (LWP 1676)):
#0  0x00007f822fab41b5 in raise () from /lib64/libc-2.12.90.so
No symbol table info available.
#1  0x00007f822fab5b66 in abort () from /lib64/libc-2.12.90.so
No symbol table info available.
#2  0x00007f822faf197b in __libc_message () from /lib64/libc-2.12.90.so
No symbol table info available.
#3  0x00007f822faf9357 in _int_free () from /lib64/libc-2.12.90.so
No symbol table info available.
#4  0x00007f8230078563 in g_free (mem=0x12c5740) at gmem.c:263
No locals.
#5  0x00007f82320c8f74 in IA__xfconf_array_free (arr=0x1295660) at xfconf.c:262
        val = 0x12c5740
        i = <value optimized out>
#6  0x0000000000408d79 in xfce_workspaces_helper_set_names (helper=<value optimized out>) at workspaces.c:366
        names_str = <value optimized out>
        i = <value optimized out>
        n_workspaces = <value optimized out>
        names = 0x1295660
        existing_names = <value optimized out>
        val = <value optimized out>
        new_name = <value optimized out>
        name = <value optimized out>
        __PRETTY_FUNCTION__ = "xfce_workspaces_helper_set_names"
#7  0x0000000000408f1e in xfce_workspaces_helper_init (helper=0x12b6330) at workspaces.c:111
        root_window = 0x1288000
        events = <value optimized out>
...

Something in setting default workspace names? 
Happy to gather more info or try patches.