error during compiling time library

I am following this tutorial to use the time and alarm library in arduino. But when i try to compile the TimeAlarmExample from the TimeAlarm library. I first got the error that WProgram.h is no present. Than after i change it with Arduino.h than i'm getting this errors which i cant remove:

In file included from /home/robot/Arduino/libraries/Time/DateStrings.cpp:10:0:
/home/robot/Arduino/libraries/Time/DateStrings.cpp:18:18: error: variable 'monthStr1' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
 char monthStr1[] PROGMEM = "January";

                  ^
/home/robot/Arduino/libraries/Time/DateStrings.cpp:19:18: error: variable 'monthStr2' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
 char monthStr2[] PROGMEM = "February";

                  ^
/home/robot/Arduino/libraries/Time/DateStrings.cpp:20:18: error: variable 'monthStr3' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
 char monthStr3[] PROGMEM = "March";

So what should i do to remove this errors?

So what should i do to remove this errors?

Do EXACTLY what the compiler is telling you. If that seems to be beyond your skill level (although I can't imagine that typing the letters c, o, n, s, and t, in the proper order is beyond your skill level), Mr Google can surely find one or more of the other 57 million posts with the same damned question in them, where the solution is spelled out.