Crucible currently (4.8) cannot anchor a patch for a file with revision "nonexistent" which is a new file which has not been committed yet. It can, however anchor patches when the revision number is revision 0.

Since there seems to have been a change in the way SVN (or Tortoise SVN) handles patches in newer SVN versions 1.9+ which are supported in modern versions of Crucible, we should be able to handle this case. (tortoisesvn - Unable to parse diff revision header 'non existent' in tortoise svn? - Stack Overflow

More details

In SVN 1.7 (and reportedly 1.8) such new files were delineated in the patch as below, being a diff with respect to revision 0, essentially:

Index: path/to/file.ts
===================================================================
— path/to/file.ts (revision 0)
+++ path/to/file.ts (working copy)

While on newer SVN versions the generated patch instead marks the file as nonexistent in the working copy, and Crucible is unable to draw an equivalence between this new notation and the previous revision 0 reference

Index: path/to/file.ts
===================================================================
— path/to/file.ts (nonexistent)
+++ path/to/file.ts (working copy)

Clarifications

Note, that it should only be able to anchor new files when the patch also contains diffs from existing files. A patch containing only new files will not be anchored.

When trying to anchor a file, Crucible will search for matches in the files in its database. Crucible will analyze all the paths in the patch, find the branches containing all those paths, then anchor the patch to the trunk or the branch with the most recent commit activity - so the path needs to have already been committed.

Workaround

Manually replace nonexistent with revision 0 before uploading the patch, for example

 sed s/nonexistent/revision 0/