As a test, I just used an old copy of FMP 5.5 to insert a jpeg that I had downloaded from the internet into a container field and it worked just fine.
Had you clicked the container field to select it before pulling down the insert menu?
Are you using a windows platform?
Does the downloaded file have the correct .jpg suffix on the file name?
It sounds like filemaker doesn't recognize the file as one with the correct format and a missing/different suffix might be the cause.
If all else fails, use a different program to open the file, select the images, and copy it to the clipboard. Now you can paste the image from the clipboard into the container field.
Thank you for your reply.
The copy pasting thing with another program did the trick.
I dont understand why it cant work the "normal" way. But hey, it works now.