Filemaker is truncating decimals on some PC's in my network (Windows NT 4.0 WS and FileMaker 5.0Nv3)

e.g. I define 2 fields as numberfields and a third as calculation: field1 + field2 and as result a number, when I enter field1= 5.9, field2 = 1.2 I get field3 = 6,00 ??? I don't use any other calculation, rounding, integer function or whatever. This also happens in some more complicated applications running on FileMaker server 5.5

When I use the same application on other PC's with another user logged on everything works ok.
When I use the same application on this other PC but with the first user logged on: the same problem.
When I delete the users NT-profile and create a new one everythings works right for some hours but then I get the same situation.
Regional setting seem to be correct and the same for all PC's

Someone out there with an idea?

thanks

Guido