Here is what I would do...

1- Log as SYS and check if package SYS.LT_EXPORT_PKG exists.
2- If package is there check if package SYS.LT_EXPORT_PKG is VALID, if not then compile it.
3- If package is there and it's VALID logout, log into the system as SYSTEM and check if offending package SYS.LT_EXPORT_PKG is visible.

Please post your findings.