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Just to report: I try to reproduce the very first example for the Dataset from the Documentation Center:

    dataset = Dataset[{
   <|"a" -> 1, "b" -> "x", "c" -> {1}|>,
   <|"a" -> 2, "b" -> "y", "c" -> {2, 3}|>,
   <|"a" -> 3, "b" -> "z", "c" -> {3}|>,
   <|"a" -> 4, "b" -> "x", "c" -> {4, 5}|>,
   <|"a" -> 5, "b" -> "y", "c" -> {5, 6, 7}|>,
   <|"a" -> 6, "b" -> "z", "c" -> {}|>}]

The message error reads: An unknown box name (TypeSystem`TypeMap) was sent as the BoxForm for the expression. Check the format rules for the expression.

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Seems to work fine on my installation; m10 on win7-64. What version/OS are you using? –  Ymareth Aug 1 at 9:19
Works for me under Linux (both, directly evaluating the example in the docs and pasting this snippet) –  sebhofer Aug 1 at 9:30
This question appears to be off-topic because the problem the user claims to be experiencing can not be reproduced. –  m_goldberg Aug 1 at 10:37
I experience this problem intermittently, but have not yet been able to determine reproduction steps. At some point in my session, this error begins to appear in all typeset Datasets, even the examples from the help. In my case, a kernel restart usually corrects the condition. V10.0.0 / Win7 / 64-bit –  WReach Aug 1 at 13:28
Mr.Wizard I think now that it is indeed a problem, but not a problem of the Dataset function as I initially erroneously assumed. I met this problem also in other situations, when after some time Mma starts to give false reactions. Usually in such cases I think that I have left something in its memory that conflicts with the operation at hand and Quit/Start the Kernel. I did not do so this time, since it was the case that I have just started Mma, and the Dataset has been first I tried. So nothing at all should have been assigned as yet. –  Alexei Boulbitch Aug 2 at 10:51

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