cannot load new themes

After I have installed wp 1.5 everything went fine until I tried some themes.
I installed five different themes (for 1.5 of course). I deleted one of them and wanted to upload this theme again. It failed. The description of the theme is not shown any more in the theme selection (the title is). The theme will not work at all. Than I tested with two other themes. All failed. Now I cannot use and install a new theme at all. They all are not working. I open one of these themes in the theme editor. The first lines are shown as follows:
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If clear the wp installation and installing wp 1.5 new it will work until I delete a theme. Any solution for this big big problem?

Thanks for your answer in advance.