UIProgressView setTrackImage and setProgressImage broke on iOS 7.1, If you are using simple flat color image for your UIProgressView, you can do this:

UIProgressView+iOS7_1

#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
#define IS_OR_GREATER_IOS7 SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"7.0")

if(IS_OR_GREATER_IOS7) {
  //specify your track color here
	[[UIProgressView appearance] setTrackTintColor:[UIcolor redColor]];
  //specify your progress track color here.
	[[UIProgressView appearance] setProgressTintColor:COLOR_2D2D2D];
} else {
  //keep your old logic here.
	[[UIProgressView appearance] setTrackImage:[UIImage imageNamed:@"img_timeline"]];
	[[UIProgressView appearance] setProgressImage:[UIImage imageNamed:@"img_timeline_highlight"]];
}