We are not aware of any bug with php 5.3 (in fact we have been using piwik on php 5.3 for years)
can you ask your hosting company what was the errror in the error log file for this 500 error? only with the error message we can figure out what is happening
can you ask your hosting company what was the errror in the error log file for this 500 error? only with the error message we can figure out what is happening