I'm using Moodle 1.9.3+ but had the same problem in 1.9.2. I'm using the latest version of the module available from the plugins page.
When I try to edit an attendance seesion and I modify the status of multiple users I get this error:
"A required parameter (id) was missing"
and nothing is updated. If I only edit the status of a single student it works without any problems.
Anyone else came across this kind of problem?