That is sufficient, but this is more correct:
Common problems arise when:
1 ) The script file is not in the directory specified. In both of our examples it must be in the same directory as the page(s) that use it.
2 ) Opening, closing and/or 'hiding' tags are left in the external file. This means that you must strip:andand their many variations from the beginning and end of the external file.
4 ) Paths to other files used by the script are no longer valid due to its location. This is only a problem if the external script is kept in a different directory than the page it was working on when it was an internal script.
5 ) Inappropriately combining two or more scripts into one external file. Usually external scripts can be combined if one knows enough about scripting to do so properly. Even then it is possible to overlook something.
A rule of thumb when testing is, if it won't work on the page, it won't work as an external file either.