I have two repositories A and B, of which B contains svn:externals to A with pegged revisions.

Whenever someone commits to A, a post commit hook notifies the Jenkins Master and a build job for B starts based on the svn:externals information.
However, the job tries to update the working copy of B to the committed revision of A.
Since the revision doesn't exist, an error occurs and the job bails out.

e.g.
Repository A: HEAD revision = 250
Repository B: HEAD revision = 100, svn:external on Repository A revision 50

Commit to Repository A which creates a new HEAD revision 251.
The master is notified through a post commit hook notification and the build for Repository B starts:

Updating http://xxx/svn/repository_b at revision 251
ERROR: Failed to update http://xxx/svn/repository_b
org.tmatesoft.svn.core.SVNException: svn: E160006: No such revision 251
svn: E175002: REPORT of '/svn/repository_b/!svn/vcc/default': 500 Internal Server Error (http://xxx)