If the path including the filename exceeds 254 characters Windows has a limitation that will not allow the file and/or directory to be created and written to.
As this is a Windows limitation you have two options;
1.) Re-install the Altiris Agent to a shorter directory path. This requires a complete re-install of the Agent as well as the Package Server and as such would cause a re-download of the full package repository when doing so.
2.) Re-create the package in a way that the maximum file-path is not exceeded. Ideas for this might be creating a ZIP file to hold the full directory structure as well as include a .bat file to perform the install commands and possibly a de-compression application to decompress the ZIP file.
You would need the .bat file to be called from the package execution command, so that you can perform more than one action. At least you would need two; One to unpack the zipfile one to perform an execution.
When using this option remember to unpack the ZIP file to a place where the maximum file-path is not exceeded as well!
The information about this limitation can be found at http://msdn.microsoft.com/en-us/library/aa365247%28VS.85%29.aspx