>How can I erase records if pack is no allowed in exclusive mode ?
I think you mean "pack is not allowed in shared mode".
You can't. You either have to kick everyone out prior to the pack so you can open the table exclusive, or devise some record recycling routine (blanking and re-using a deleted record instead of appending a new record.)
Packing shouldn't need to be done that often. Too many deleted records can effect performance, but there are few situation where it needs to be done daily -- and a situation like that might call for record recycling.
I usually build in a way to kick users out of the application from an administrative menu in case the system admin needs to pack or reindex. Some poeple also set a timer to perform packing, reindexing and other admin functions in the middle of the night when everyone is logged out.
HTH