[Typo3] [Typo3] Fatal error: Cannot redeclare class (version 3.6.0) (php 4.1.2)

[W van Bruggen]

Hello list,

i've just made a small plugin which gets the info from the headerfield
and adds it to a variable that constructs the path to a certain
directory. The first time i loaded the plugin and checked it out it
worked fine. I wanted to make some modifications, changed the class
file and wanted to see how my changes worked out.

Surprisingly i get this error : 
"Fatal error: Cannot redeclare class in (path to *pi1.php file) in line 34"

Line 34 says this :
class tx_stocksdirectory_pi1 extends tslib_pibase {

Anyone ever had the same error and knows a fix ?

greets,
Wietse van Bruggen