Some users experience blocking dialogs indicating that IPTC metadata cannot be included in one or more versions during export.
Two potential causes exist:
1. RAW+JPEG Pairs with JPEG as Master
The solution involves searching your Aperture library for RAW+JPEG pairs (using smart albums) and configuring Aperture to use the RAW file as the master instead.
2. JPEG Incompatibility with Aperture Metadata
Investigation reveals that certain JPEG files are "incompatible" with Aperture's metadata writing capabilities. This is neither a permissions issue nor a library problem. Some JPEGs cannot have IPTC metadata written to them by Aperture, even when using Aperture's native metadata writing function. The incompatibility cannot be determined before attempting export.
Creating metadata sidecars for all JPEGs would prevent export problems, but Lightroom does not utilize sidecar files for JPEG images, creating a circular problem.
An alternative solution using exiftool is documented in the related article "The Mystery of Aperture Not Able to Embed Metadata Into Some JPEGs."
The blocking messages cannot be suppressed as they originate from Aperture itself.