Symptom:
File transfer/file creation will fail and print the error message No more root directory entries available when the maximum number of files within the root directory of the compact flash is reached and a new file transfer /creation attempt occurs.  Any further attempt at file transfer/creation to the flash will fail regardless of what process transfers/creates the file.

Conditions:
Regardless of the total remaining free space on the compact flash this issue will occur when the root directory contains 252 files and a file transfer/creation attempt occurs (examples below).  

The file test-file.txt is 1KB in size.

File copy:

CF-Test# copy ftp://username:password@10.10.10.10/CF-Test/test-file.txt flash:
Destination filename [test-file.txt]?
Accessing ftp://*****:*****@10.10.10.10/CF-Test/test-file.txt
Loading CF-Test/test-file.txt!
[OK - 612/4096 bytes]
%Error opening flash0:/test-file.txt (No more root directory entries available)


Show command redirect attempt (File creation):

CF-Test#show version | redirect flash:version.txt
%Error opening flash0:version.txt (No more root directory entries available)
CF-Test#
000031: *Aug 17 16:50:30.655: %PARSER-3-URLOPENFAIL: cannot open file for redirection 'No more root directory entries available'

Output of show flash displaying capacity:

CF-Test#sh flash:
-#- --length-- -----date/time------ path
1     99098648 Jun 26 2014 10:43:10 +00:00 c2900-universalk9-mz.SPA.154-2.T1.bin
<snip>
252    100000   Aug 6 2014 20:57:16 +00:00  Test-File252.txt 
260153344 bytes total (37146624 bytes free)