Grid problems

I am writing a program to enroll students and  I'm having a big problem. i am using a datamodule in which I put all my tables. If I enroll students i alter my course and student table. They are linked on each other with a nr ( key in student) Student is the master table. When i couple 2 Dbnav on these tables and there is more than one course for one student I get an EInvalidGridOperation =>> Grid index out of bounds/date/invalid. I solved this by putting two table componenets on the form where this is necessary and now it works. What causes this problem???
Please help me, it's for my final report....
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javiertbConnect With a Mentor Commented:
I've experienced the same problem some times and it seems to be one of those Delphi bugs, but here you have several options which may help you:

   -Do not link at definition time more than one form to the same     DataSet.

   -Before making that call to the last record, set the         datasource Enabled property to false, then set it to True     after calling Last record. If you're looping through several     records at a time, set the Enabled property prior to entering     the loop and reset it after leaving the loop.

   -If you have hidden grids (for example on other tab pages) you     may get the error when the database gets to the end. The     easiest way to avoid the error is to use the onshow events of     the tab pages or forms to enable the grid and the onhide     event to disable the grid, this way the error doesn't seem to     happen.

I've been also talking with people about the same proble and they got to solve it by checking what I stated before.

Hope this helps
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