I'm not using 5.1.4 myself yet. I recall reading somewhere that the .htm files (web interface...etc...)were updated.
Solution:
Get the CVS version of eAccelerator.
Un-tar or Un-zip the files and look at the control.php file. The new control panel for eAccelerator.
Try to avoid dealing with password protection with EA until you have it working. I'm not sure this is still an option with 0.9.5CVS.
Then once you have it working introduce the password protection feature.

Also it looks like now we have a new variable "eaccelerator.allowed_admin_path "

Here is an extract of the readme file with CVS 0.9.5 (05_23_2006):
".../...
If you want to use the control-panel you need to compile eAccelerator with
--with-eaccelerator-info which is the default value.
You need to copy the control.php file to your webroot and set the path to it
in the php.ini or eaccelerator.ini in the eaccelerator.allowed_admin_path
directive. If you don't do this you wont be able to see much information and
can't control eAccelerator.
You can set the username and password needed to access the control-panel in
the control.php file.

When you compile eAccelerator with --with-eaccelerator-disassembler you need
to place the dasm.php file also in the same directory as the control.php file.
You can set the username and password needed to access this file at the top
of the file.
.../..."

Hope this helps...