conor100, looking at the code [arduino-1.5.3]\hardware\arduino\x86\libraries\WiFi\WiFi.cpp the beign method has 3 implementations:
begin(char* ssid, uint8_t key_idx, const char *key)
begin(char* ssid, const char *passphrase)
You are using the the third which is for WPA/WPA2, if your WiFiis open then change it to the first one, if your WiFi is set to use WEP then use the second implementation.
Thanks very much for your help.