I am sorry that you got problem with activities
Activity locking is only a hack and it use some of original moodle files slightly modified. That is why it is very sensitive to the moodle version implied.
It is not uninstallable and non downgradable.
If you try to install it a second time it will not be able to do things like ALTER TABLE `prefix_course_modules` ADD `delay` VARCHAR( 10 ) NOT NULL AFTER `added `
because the table was probably altered in the first attempt to install activity locking.
For your particular case you seem to have try to install Activity_Locking_for_Moodle_1.7_.zip in a 1.7.2+ version of moodle wich are incompatibles.
If you check carefully from moodle plugins
you will see that recent 2 versions exist one for 1.6 only and the other for 1.7.1 only and they cannot be intermixed.
Another reference is that table
wich specify that many versions exist but none for 1.7.2. The version you use is specific for 1.7 only.
I hope you did'nt installed it on a production server as stated in all versions!
Destroy database and try a fresh new install of moodle 1.7.1
with activity locking for 1.7.1 only
and it will work as stated the first time!
I hope it may help,Bernard