Graphs created using Prism Graph software can not be exported or copied and pasted into PowerPoint. The graphs will appear in the print preview, but will not print.
The graph must be saved as a picture file, then inserted into PowerPoint as a picture.
Copy graphs from the Prism Graph software, paste into Photoshop, Microsoft Paint or other image editing software and save as a jpeg file. Use the Insert > Picture > From File... function of PowerPoint to insert the jpeg file into the poster.
If the graph is in another PowerPoint application, right click on the graph and save it as a picture file, then copy the picture file back into the poster.