Unable to save array to NSUserDefaults -

this first attempt @ using nsuserdefaults. i've read every question & answer posted in stackoverflow regarding subject, still can't work. must missing basic. array (allcontacts) merely contains few names , phone numbers. unless i'm misunderstanding what's happening, both fields nsstrings. or pointers strings? if that's case, how convert them actual nsstrings? here's code save array:

- (bool)savechanges {     nsmutablearray *mutablearray = [[nsmutablearray alloc] initwitharray:allcontacts];     [[nsuserdefaults standarduserdefaults] setobject:mutablearray forkey:@"allcontacts"];     [[nsuserdefaults standarduserdefaults] synchronize];     return 1; } 

here log:

2013-08-07 15:48:17.568 imok[5515:907] *** -[nsuserdefaults setobject:forkey:]: attempt insert non-property value '(     "brad pitt, 1-917-297-1234",     "marilyn monroe, 9179291234" )' of class '__nsarraym'.  note dictionaries , arrays in property lists must contain property values. 

thanks in advance help.

this code "for(id contact in allcontacts) { nslog(@"%@", [contact class]); }" gives me:

2013-08-07 17:11:30.845 imok[5569:907] contacts 2013-08-07 17:11:30.854 imok[5569:907] contacts 

so guess not valid property values. incidentally, there no intelligent reason me attempt save array nsmutablearray. experimenting.

from apple documentation: https://developer.apple.com/library/mac/#documentation/cocoa/reference/foundation/classes/nsuserdefaults_class/reference/reference.html#//apple_ref/doc/c_ref/nsuserdefaults

a default object must property list, is, instance of (or collections combination of instances of): nsdata, nsstring, nsnumber, nsdate, nsarray, or nsdictionary. if want store other type of object, should typically archive create instance of nsdata.

if allcontacts nsarray, use in setobject:forkey: call. if it's nsmutablearray, use:

[allcontacts copy]

to non-mutable copy of array.