Problem when using functionality Book List in TEM

Hello

We've encountered a problem when making bookings in TEM.

When using the functionality Book list in PSV1 or PSV7 there is an error message that says "Business event E nnnn is currently locked; try again later".

One or several attendees will become booked but not the whole list.

I recently changed working area so the whole TEM part is a new world to me, all ideas on solution is welcome!!

/Andreas