Arduino won't get programmed

I was burning a program to read inputs from a sensor and drive a speaker if the input would fall below a threshold and was also monitoring the input on the serial monitor. After a few times of running the code suddenly Arduino refused to pragram. I restarted my computer and tried again but still it won’t program. Can anybody interpret the error that I have posted below and tell me what is the matter.

Also, the last program that I had burnt is still working on the arduino.

processing.app.SerialException: Error opening serial port '/dev/ttyACM1'.
	at processing.app.Serial.<init>(Serial.java:146)
	at processing.app.Serial.<init>(Serial.java:76)
	at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:75)
	at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:93)
	at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:56)
	at processing.app.Sketch.upload(Sketch.java:1603)
	at processing.app.Sketch.exportApplet(Sketch.java:1568)
	at processing.app.Sketch.exportApplet(Sketch.java:1524)
	at processing.app.Editor$DefaultExportHandler.run(Editor.java:2293)
	at java.lang.Thread.run(Thread.java:636)
Caused by: gnu.io.UnsupportedCommOperationException: Invalid Parameter
	at gnu.io.RXTXPort.setSerialPortParams(RXTXPort.java:171)
	at processing.app.Serial.<init>(Serial.java:136)
	... 9 more
processing.app.debug.RunnerException: Error opening serial port '/dev/ttyACM1'.
	at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:99)
	at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:93)
	at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:56)
	at processing.app.Sketch.upload(Sketch.java:1603)
	at processing.app.Sketch.exportApplet(Sketch.java:1568)
	at processing.app.Sketch.exportApplet(Sketch.java:1524)
	at processing.app.Editor$DefaultExportHandler.run(Editor.java:2293)
	at java.lang.Thread.run(Thread.java:636)

Sorry everyone. Got the solution here.

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1228315338

Try editing your Arduino preferences file (~/.arduino/preferences.txt I think) and setting the serial.debug_rate to, say, 9600. (serial.download_rate should be 19200).