ProxyCacheException: offset < 0: -2147476036

The code that caused the exception at com.danikula.videocache.file.FileCache.available(FileCache.java:46)

//old code ：
@Override
public synchronized long available() throws ProxyCacheException {
try {
return (int) dataFile.length();
} catch (IOException e) {
throw new ProxyCacheException("Error reading length of file " + file, e);
}
}

//change code
@Override
public synchronized long available() throws ProxyCacheException {
try {
long fileSize = dataFile.length();
return fileSize;
} catch (IOException e) {
throw new ProxyCacheException("Error reading length of file " + file, e);
}
}

this is error log:
com.danikula.videocache.ProxyCacheException: Error writing 8192 bytes to java.io.RandomAccessFile@530f0a3 from buffer with size 8192. Version: 2.7.1
at com.danikula.videocache.file.FileCache.append(FileCache.java:73)
at com.danikula.videocache.ProxyCache.readSource(ProxyCache.java:132)
at com.danikula.videocache.ProxyCache.access$100(ProxyCache.java:19)
at com.danikula.videocache.ProxyCache$SourceReaderRunnable.run(ProxyCache.java:187)
at java.lang.Thread.run(Thread.java:919)
Caused by: java.io.IOException: offset < 0: -2147476036
at java.io.RandomAccessFile.seek(RandomAccessFile.java:612)
at com.danikula.videocache.file.FileCache.append(FileCache.java:69)
at com.danikula.videocache.ProxyCache.readSource(ProxyCache.java:132) 
at com.danikula.videocache.ProxyCache.access$100(ProxyCache.java:19) 
at com.danikula.videocache.ProxyCache$SourceReaderRunnable.run(ProxyCache.java:187) 
at java.lang.Thread.run(Thread.java:919) 

com.danikula.videocache.ProxyCacheException: Error writing 764 bytes to java.io.RandomAccessFile@530f0a3 from buffer with size 8192. Version: 2.7.1
at com.danikula.videocache.file.FileCache.append(FileCache.java:73)
at com.danikula.videocache.ProxyCache.readSource(ProxyCache.java:132)
at com.danikula.videocache.ProxyCache.access$100(ProxyCache.java:19)
at com.danikula.videocache.ProxyCache$SourceReaderRunnable.run(ProxyCache.java:187)
at java.lang.Thread.run(Thread.java:919)
Caused by: java.io.IOException: offset < 0: -2147476036
at java.io.RandomAccessFile.seek(RandomAccessFile.java:612)
at com.danikula.videocache.file.FileCache.append(FileCache.java:69)
at com.danikula.videocache.ProxyCache.readSource(ProxyCache.java:132) 
at com.danikula.videocache.ProxyCache.access$100(ProxyCache.java:19) 
at com.danikula.videocache.ProxyCache$SourceReaderRunnable.run(ProxyCache.java:187) 
at java.lang.Thread.run(Thread.java:919)