PhotoPlus X5: Copying and pasting a large GIF as a layer crashes Photoplus X5

[driversoft]

I've created a large GIF file (approx A1 size at 300 dpi, around 230K when saved) to use as a mask for an underlying image - attempting to add this GIF as a layer to any other image (including itself) using either Ctrl C and Ctrl L (or the menu equivalents) always crashes PhotoPlus with a fairly nonsensical error message in the app C:\\...

Further, Photoplus refuses to load any A0 300 dpi standard JPG images I've created, and gives a generic error message. I accept these are big images, but I know they are valid - Photoshop loads them, as does Windows Preview - so where is the limitation - is it in Photoplus itself, or my 6 Gigs of memory?

Sony Laptop, 64 bit AMD Phenom triple core processor, Windows 7, 6 Gbyte memory.