The PDF report generator will require a lot of memory especially if there is a large amount of photos or videos. It is recommended to have at least 16GB of RAM and also at least 32GB of free space on system disc for temporary data swapping. If it is still not enough, we recommend the following:
Choose 'PDF Report - Multiple files' so the final PDF is not too large and the generation process doesn't require so much memory. It will split the report into multiple PDFs, by data categories.
Generate HTML, Excel or UFED (available from MOBILedit Forensic Express version 3.5).
If there is an extremely large number of images we recommend turning them off for the first round of exporting and selecting the MOBILedit Backup together with PDF Report - Multiple files. In the second round you just open the MOBILedit Backup file, without needing the phone, and running only the analysis of media. (by Generating MOBILedit Backup format, you can repeat data parsing without having the phone itself)
Please find more info on all the possible report formats here.