As per Microsoft: "The Staging Directory is an area where modified files are stored temporarily either before being propagated to other replication partners or after being received from other replication partners. FRS encapsulates the data and attributes associated with a replicated file or directory object in a staging file. FRS needs adequate disk space for the staging area on both upstream and downstream machines in order to replicate files". See the link to "Troubleshooting File Replication Service" for details on this event.
See the link to "EventID 13522 from source FRS" for details on this event.
describes a way to calculate how much space you might need. Itís a good reference article.
shows possible causes of a Full File Replication Service Staging Area.
As per Microsoft, the File Replication Service (FRS) for Microsoft Windows 2000 uses a "staging area" for replication. The default size of the staging area for FRS is approximately 660 megabytes (MB). If you want to replicate data that exceeds this amount, you may need to configure the FRS staging area to accommodate additional drive space. In addition, the volume that contains the staging area must also have this same amount of additional drive space available.
You may also relocate the staging folder (frs-staging) to a drive with more free space. Instructions are in KB article ME265085