ProvideX 7.71 for SCO6 was released a very long time ago and at the time there were some issues with EFF files handling large updates.
Since ProvideX 7.71 is no longer supported (nor do we support SCO) we would suggest you upgrade to PxPlus and probably transition to something like Redhat Linux (or Centos, Oracle Linux) or Debian (Ubuntu).
The transition to PxPlus will allow you to have files (both VLR and EFF) > 2GB while switching to Linux will likely provide you a faster platform with more options for future development.
As for your question about ProvideX supporting files > 2GB, you indicated that you had a 4GB file already which indicates it does.