Magento – Product Images not shown after uploading , how

So after a day of diving into this issue; disabling modules, enabling modules, removing changes in local etc etc, I found the problem.

I used an extension called PhPro_Translate to do a large amount of translations for front and backend from English to Swedish and so in my std install I have just inserted all the rows of translations into core_translate (as the extension does). It turns out that one of the 80 or so translated strings under the Mage_Cms module cause the error. I honestly did not have the energy to look into exactly which string as I still have 3400 rows working :), but I have a vague idea it could have been a Swedish word with umlauts.

In the very unlikely event that someone else runs into the same problem, that's the answer!

Cheerio

UPDATE: Since this could have implications in other contexts, here's what caused the js error. In one of the translations I had used single quotes around a word to denote it was the original English term but I had forgotten to escape the quotes. Voilà!

This looks like an upload size issue.
Even if it's stated in the comments that the value in php.ini has been changed, check if you modified the right php.ini. A fast way to check the max size of the uploaded files is to go to System->Import/Export->Import.
You should see a message at the top of the page saying:

Total size of uploadable files must not exceed ....M