[Solved] Problems with output

Hi

I have a document where I have inserted several graphs. I have a folder accessible from the path where the graphics are stored. When I export to pdf the following error emerges.
Error: pdf_hummus, failed to create Form from PNG stream
Error: failed in end PDF

The pdf is then not readable from adobe acrobat whereas it is accessible from sumatra

I have graphs in jpg and png.

Any guess about where is the failure?

Thanks

Solved.
One of the graphs was a gif. when exported to png the problem disapeared

Thanks anyway Hope this helps someone else