Error #1034 Hell

I just had the weirdest problem with FlashEff2. It's hard to describe but easy to reproduce (at least for me).

I've had a Flash file with multiple FlashEff Components, all was fine.

But then, as soon as I've added another component, I've got an Type Error: Error #1034. I've added text, applied a text effect and I got the error. I've added a symbol, applied a symbol effect and I got the error. I've deleted the component in question, heck, I've even deleted the whole layer and re-added it and I've still got the error.

Now here is the weird thing: if I used a different symbol out of my library - it worked. But there was nothing wrong with the symbol I've used before. I know, because I've double checked that symbol in a different file.

Here is the workaround I've stumbled upon: I wasn't able to add a new effect - but I was able to copy a frame with an effect in it to a new layer and then edit that effect. Very weird.