Log error with Snapshot: what does it mean ?

Hi,

When I use snapshot, it looks as if it worked ok ("Archives: Complete") but when I have a look at the log there are several erros:

2013-11-27 16:43:31: init
2013-11-27 16:43:32: Notice: errno:8 Undefined index: global_user_ids /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2943
2013-11-27 16:43:32: Warning: errno:2 join(): Invalid arguments passed /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2943
2013-11-27 16:43:32: Notice: errno:8 Undefined index: global_user_ids /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2944
2013-11-27 16:43:32: Warning: errno:2 join(): Invalid arguments passed /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2944
2013-11-27 16:43:32: Notice: errno:8 Undefined index: global_user_ids /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2937
2013-11-27 16:43:32: Warning: errno:2 join(): Invalid arguments passed /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2937
2013-11-27 16:43:32: Notice: errno:8 Undefined index: global_user_ids /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2938
2013-11-27 16:43:32: Warning: errno:2 join(): Invalid arguments passed /home/xxx/public_html/wp-content/plugins/snapshot/snapshot.php on line 2938

What to think about it?

Best Regards