Why does one statement work and one not - ios

Question

I have a table in a database which I access like this:
+(NSMutableArray *) queryDatabaseWithSQL:(NSString *)sql params:(NSArray *)params {
sqlite3 *database;
NSMutableArray *rtn = [[NSMutableArray alloc] init];
int index = 0;
NSString *filepath = [self copyDatabaseToDocumentsWithName:#"database"];
if (sqlite3_open([filepath UTF8String], &database) == SQLITE_OK) {
const char *sqlStatement = [sql cStringUsingEncoding:NSASCIIStringEncoding];
sqlite3_stmt *compiledStatement;
if (sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
if ([params count]) {
for (int i = 0; i < [params count]; i++) {
NSString *obj = [params objectAtIndex:i];
sqlite3_bind_blob(compiledStatement, i + 1, [obj UTF8String], -1, SQLITE_TRANSIENT);
}
}
while (sqlite3_step(compiledStatement) == SQLITE_ROW) {
NSMutableArray *arr = [[NSMutableArray alloc] init];
index = 0;
const char *s = (char *)sqlite3_column_text(compiledStatement, index);
while (s) {
[arr addObject:[NSString stringWithUTF8String:s]];
index++;
s = (char *)sqlite3_column_text(compiledStatement, index);
}
if (![rtn containsObject:arr]) {
[rtn addObject:arr];
}
}
}
sqlite3_finalize(compiledStatement);
}
NSLog(#"ERROR: %s", sqlite3_errmsg(database));
sqlite3_close(database);
return rtn;
}
This works fine when I call the function like this:
NSLog(#"%#", [database queryDatabaseWithSQL:#"SELECT * FROM FRIENDSUSERS WHERE USER = ?" params:#[[delegate->user objectForKey:#"username"]]]);
Then when I call the function using a string like this it doesn't return any rows:
NSLog(#"%#", [database queryDatabaseWithSQL:#"SELECT * FROM FRIENDSUSERS WHERE USER = ?" params:#[#"username"]]);
I haven't got a clue what is going one with but I have checked the strings match and they do so I'm now stuck
Can anyone see any reason why this would not work
I have run error checks as well and every time it returns no error, or rows :(
Thanks in advance