Attempts to write to the same log file within one batch script results in: The process cannot access the file because it is being used by another process.

All -

I've been trying to setup an automated process on our Windows 2003 server.  I'm running this batch scripts:

@echo off
set CCM_HOME=c:\progra~1\ibm\rational\synergy\7.2
set PATH=%path%;c:\progra~1\ibm\rational\synergy\7.2\bin
REM Put a file down so people know that update is in progress
echo . >> D:\TCP_WORK_AREA\UPDATE_IN_PROGRESS.txt
REM Put some newlines and thre current date/time in the log file
echo . >> D:\TCP_WORK_AREA\update_log4.txt
echo . >> D:\TCP_WORK_AREA\update_log4.txt
echo %DATE% %TIME% >>  D:\TCP_WORK_AREA\update_log4.txt
REM funny synax >> <FILENAME> 2>&1 redirects both STDOUT and STDERR to log file (use of double angle brackets appends rather than overwrites)
REM Make sure the @ symbol directories are in place for Synergy
echo "Renaming CSI_CORE Dirs For Synergy" >> D:\TCP_WORK_AREA\update_log4.txt
perl D:\TCP_WORK_AREA\CSI_EXTERNAL_UTILS\0.0\CsiSynergyUtils\renameDirsForSynergy.pl D:\TCP_WORK_AREA\CSI_CORE >> D:\TCP_WORK_AREA\update_log4.txt 2>&1
perl UPDATE_TCP_WA.pl >> D:\TCP_WORK_AREA\update_log4.txt 2>&1
echo "Running Setup Subprojects!" >> D:\TCP_WORK_AREA\update_log4.txt
cd D:\TCP_WORK_AREA\CSI_EXTERNAL_UTILS\0.0\CsiSynergyUtils
perl -I "D:\TCP_WORK_AREA\CSI_EXTERNAL_UTILS\0.0\CsiSynergyUtils" subProjectSetup.pl \\astvden-amslab\TCP_WORK_AREA >> D:\TCP_WORK_AREA\update_log4.txt 2>&1
echo "Renaming CSI_CORE Dirs For MATLAB" >> D:\TCP_WORK_AREA\update_log4.txt
perl D:\TCP_WORK_AREA\CSI_EXTERNAL_UTILS\0.0\CsiSynergyUtils\renameDirsForMatlab.pl D:\TCP_WORK_AREA\CSI_CORE >> D:\TCP_WORK_AREA\update_log4.txt 2>&1
echo "Stopping Synergy Session" >> D:\TCP_WORK_AREA\update_log4.txt
ccm stop >> D:\TCP_WORK_AREA\update_log4.txt 2>&1
REM All done so remove the UPDATE_IN_PROGRESS file
del D:\TCP_WORK_AREA\UPDATE_IN_PROGRESS.txt

Everything runs fine up to 17, when the script dies with the message: "The process cannot access the file because it is being used by another process".  Afterwards, subsequent calls to this script will die immediately with the same message until I change the log file name.  I've been stumped by this one, because there's no other scripts running and no other processes that should have update_log4.txt open.  Although now that I'm writing this up , I noticed that I do CD to another directory just before line 17.  Would that cause problems like this?