Problem with Wire and endTransmission

I have some I2C code that worked fine until a few days ago.
After some troubleshooting, it appears that the Wire.endTransmission(); is never returning.

With the following code from Wire examples, I never see the “after end transmission” statement.

#include <Wire.h>

void setup()
  Wire.begin(); // join i2c bus (address optional for master)

byte x = 0;

void loop()
  Wire.beginTransmission(4); // transmit to device #4
  Wire.send("x is ");        // sends five bytes
  Wire.send(x);              // sends one byte  
  Serial.println("Before end transmission");
  Wire.endTransmission();    // stop transmitting
  Serial.println("after end transmission");


avr-gcc --v
Using built-in specs.
Target: avr
Configured with: …/src/configure -v --enable-languages=c,c++ --prefix=/usr/lib --infodir=/usr/share/info --mandir=/usr/share/man --bindir=/usr/bin --libexecdir=/usr/lib --libdir=/usr/lib --enable-shared --with-system-zlib --enable-long-long --enable-nls --without-included-gettext --disable-checking --disable-libssp --build=i486-linux-gnu --host=i486-linux-gnu --target=avr
Thread model: single
gcc version 4.3.2 (GCC)

gcc --v
Using built-in specs.
Target: i486-linux-gnu
Configured with: …/src/configure -v --with-pkgversion=‘Ubuntu 4.3.3-5ubuntu4’ --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr --enable-targets=all --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4)

Any ideas ?