I just tried it again on a number of different PC's with different setups and with different browsers and it worked for me every single time.
What I find awkward, is that you say you get the validator message, yet the product is still saved. That shouldn't be possible if you consider this code:
If Page.IsValid Then
myProduct.Title = txtTitle.Text
myProduct.TagLine = txtTagLine.Value
myProduct.Description = txtDescription.Value
myProduct.Keywords = txtKeywords.Text
As you can see, the Save method can only be called when the page is valid. Can you provide more details about what you do? What's the address in the address bar? What browser do you use? Do you see the FCKeditor appear? Do you have this problem with editing existing products too or only with new items?
Sorry for the many questions, but I don't see a solution to your problem at this stage.
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