I came across this code to make a list of all installed packages and the write it to a text file if you want it to. The problem is that sometimes the code works and sometimes it doesn't. I can't figure out why it doesn't work sometimes. The code is:

./user_installed_packages

When it doesn't work I get the following error message: bash: ./user_installed_packages: No such file or directory

Any thoughts or ideas as to what could be causing it? I'm running Xubuntu 12.04 64-bit.