求助编译错误

wdb_9955

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String myData = "";
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myData = mySerial.read();
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......
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Arduino:1.5.5-r2 (Windows XP), 板："Arduino Uno"

sketch_jan15c.ino: In function 'void loop()':
sketch_jan15c:18: error: ambiguous overload for 'operator=' in 'myData = mySerial.SoftwareSerial::read()'
C:\Documents and Settings\Administrator\桌面\arduino-1.5.5-r2\hardware\arduino\avr\cores\arduino/WString.h:86: note: candidates are: String& String:perator=(const String&) <near match>
C:\Documents and Settings\Administrator\桌面\arduino-1.5.5-r2\hardware\arduino\avr\cores\arduino/WString.h:87: note:                 String& String:perator=(const char*) <near match>
C:\Documents and Settings\Administrator\桌面\arduino-1.5.5-r2\hardware\arduino\avr\cores\arduino/WString.h:88: note:                 String& String:perator=(const __FlashStringHelper*) <near match>

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这个错误是什么意思？先谢了！