Version 4.3.4.3 solves a long standing issue: before this update it was impossible to upload big sources, and users had to limit their imports to 3-4000 items per source. In the Forum archive, you'll find plenty of messages giving advice on how to subdivide single large RIS files into smaller ones. Starting from today, the previous advice is outdated, and can be safely ignored in most cases.
From now on, it is not necessary to subdivide RIS files if they contain 15000 items or less. If your files are bigger than that, you can still try, but be aware that (depending on the power of your local computer), EPPI-Reviewer may get overwhelmed by too much information and either take a long time to "read" the file, or freeze and stop responding. If this happens, closing the browser and logging on again will solve the immediate problem and you will still need to subdivide the large source file.
How does this work?
The text-based Source Import has been largely re-written. The new system will detect if a source is likely to be too big to be sent to the server in one go, and will automatically send it across in smaller chunks. The main effect is that there is no need to manually subdivide large import files anymore.