The Macintosh IIfx has a special serial port which works in "faster mode" by using a buffer. This can cause connection problems when using the ClarisWorks communication environment. Older modems are particularly problematic in conjunction with the "faster mode."
There is an freeware INIT, available from users groups, AppleLink and BBSes, called Serial Switch. This control panel device will allow the serial port to be switched to its slower, more conventional mode. This may or may not fix the problem, but is a good first step for IIfx owners experiencing connection problems.