I hope this wasn’t stuck for 9 years
In any case, rundll32 would have been triggered by whatever content was in the action you ran, to be clear this isn’t the BES client itself locking the folder.
To troubleshoot, the ‘handles.exe’ utility from Sysinternals (https://microsoft.com/sysinternals) is very “handy” for identifying which process has any given folder/file locked, and the same tool suite’s ‘pskill’ is handy for killing the offending process.
Per the release announcement for BigFix 9.5.11 earlier this week, there is now a native method for the BESClient to kill child processes after waiting for a time-out period. I’m excited to try out this feature, it’s a feature for which I’ve lobbied. RFE’s work!