You should be able to load a Motif XF .X3A file directly to MONTAGE as a LIBRARY.
Place the USB stick in the TO DEVICE port
Press [UTILITY] > touch "Contents" > "Load"
Set the "Content Type" = LIBRARY FILE
Touch the box that represents your "USB DISK_usb1_1"
Find your .X3A and touch the file to execute the LOAD

If you already have Libraries installed then you must have an available Library slot and enough memory remaining to accommodate what you are attempting to install. If not, you will receive a Sample Memory Full message.
You can view how much of your Sample Memory is used by navigating to your WAVEFORM folder:
[UTILITY] > "Contents" > "Data Utiliy" > touch the "Waveform" folder; You Sample Memory used out of 1.8GB will be shown in the upper right corner.
Verify you have enough memory left before loading the file.

Memory works as follows:
approx 1.75~1.8GB total Sample Memory
2048 Waveforms per Library
Approx 8192 Samples per Library

Memory is basically filled on a which ever limit is reached first. If you run out of Sample slots before you use all the memory, you are still out of memory. If you exceed the number of Waveforms before you use all of the memory you are still out of memory...

Hope that helps.

Thank you bad master,
I have just used 2.2MB out of 1.8GB,My file is 570MB,Still plenty of space I I don't know why this is still saying out of memory .Is any way to increase internal memory ?
I tried deleting all file I which loaded but the result is same

Where was the file created? In the Motif XF or in the Melas Editor?
Remember if you exceed the number of Samples even before you fill the 1.75GB it will report you’re out of memory. If you exceed the number of Waveforms even before you fill the 1.75GB it will report you’re out of memory.
Do you know how many Waveforms and how many Samples you are attempting to load?

I was just wondering how to do this myself. I was about to buy some third-party libraries for my Montage soon, but wasn't sure how I would load them and if I would be able to organize them in the Montage's resident memory (some of the libraries are for the Motif XF and a few are Montage-specific). I think Bad Mister's post above explains it pretty clearly—thanks!

Most third party developers (those worth buying from) will have tested their sound libraries so that they load into the product they are designed for. I do not recall any third party libraries that exceeded 1GB of data (never) - it is highly unlikely that a third party library would exceed the product it was designed for... that is why I asked if it were a user creation as opposed to one commercially available. A User Library is more likely to exceed the boundaries of the instrument, because the goal is load everything they have obtained.... where a commercially available library would strive for compatibility at all costs and fit just what they are selling.