Webstar, FMP 4, Lasso 3.6 crash

I have this situation:

My Web server on Mac G3-266 with:

Webstar 4.4

Lasso 3.6.6

FMP 4.1 (normal)

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1 FMP 4.1 for Windows on PC for updating

FMP serve a very large db with 2 small relational files, with script, schedule, etc.

There is a client with FMP 4 for windows that update the FMP 4 for Mac on Web via TCP/IP and Lasso sharing the db on Web. It works from two years but from four months FMP 4 for Mac (on the Web server) goes to crash and it happen not always but sometimes when the client FMP 4 for Windows is connected (not always): the FMP client goes to loop for finding some data in FMP 4 on Web server: it crashes the FMP 4 for Mac. I have to force quit FMP 4 on Mac side (ctrl+alt+command+ESC). This error is random: it does not happen when FMP 4 for Win is not connected: it's strange for me because the server is stable.

What are the causes ? Speed, FMP protocol..... Is it OK to use an FMP client for updating or I must to create lasso pages for updating?

Who help me ?