since now i got no problem with miktek(2.4) and metapost but today i started writing a metapost file with a "btex $\mathcal{}$ etx" command and Metapost refuses to make a .mpx file, saying that :

"the two files given above are one of your source files and an auxiliary file i need to read to find what your btex...etex block means..."
Can you help me please.