At first, check is any filter used for calls window. It is possible that calls are not showed because they are not matching filter requirements. Check also isn't option Freeze calls list selected. In case it is, you get no new calls until unchecked.
If you've already made sure that both filter and Freeze calls list are not set, and calls still not showing on the list, it is necesary to check are active calls storing to database.
For this purpose it would be easiest to open VSM->Settings->Voipswitch and check Active calls recording card. At least 1 main option should be selected, but best practice is select all there. Such change may require to reload switch settings or even restart it.
In case, after all previously described activities didn't fix the problem, consider that calls table may consist incorrect columns. Please make sure calls are stored to database. In case when there's a problem with DB structure, Voipswitch should show MySQL errors in Logs section. If you have any there, it will be best to contact our support to check structure of currentcalls table.