Image size causing 500 Internal server Error

[color=#000000]Using CS-CART: version [/color]2.1.4 PROFESSIONAL


[color=#333333][font=Arial, Helvetica, sans-serif][size=3]When we are trying to add new products with bigger image size (700W x 500H) we are getting error as below[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]Internal Server Error[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]The server encountered an internal error or misconfiguration and was unable to complete your request.[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]Please contact the server administrator and inform them of the time the error occurred, and anything you might have done that may have caused the error.[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]More information about this error may be available in the server error log.[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]--------------------------------------------------------------------------------[/size][/font][/color]

At same time [font=Arial, Helvetica, sans-serif][color=#333333][size=3]if we use[/size][/color][/font][color=#333333][font=Arial, Helvetica, sans-serif][size=3] the same image in smaller image size (ex 495 x 481) we do not get any error[/size][/font][/color]

[color=#333333][font=Arial, Helvetica, sans-serif][size=3]Appreciate if someone can guide what can be the issue. Using Plesk 10.4.4[/size][/font][/color]