Problem compiling project in Eclipse

Hello, and many thanks for this great app.
My question, as the title says, is related to Eclipse.
After importing the project into an eclipse workspace (Eclipse Pulsar, updated Android SDK) there seems to be compile erros in two files.

OAuthKeyFetcher.java
public int execute(...) {
...
url = new URL(context.getString(R.string.mustardoauthkeyurl)+"?"+MustardApplication.sVersionName);
--> mustardoauthkeyurl cannot be resolved or is not a field
...
}

Twitpic.java
public static String upload(...) {
...
params.add(new BasicNameValuePair("key", context.getString(R.string.twitpic)));
--> twitpic cannot be resolved or is not a field
...
}

It seems to be a problem with the SDK. Neither of the suggested "quick fixes" works, as they modify the generated R file.

Any clue on this? It's my first Android/Eclipse development test.
Thanks in advance!