Hmm, one more example of the "new" symbolic engine which was introduced with Prime 6 having quite some flaws and being inferior compared to the old one (muPad), which in turn was far away from being perfect or even competitive with Maple or Mathematica.
You may consider reporting this bug to PTC support.
Prime 6 is the only version where we still could switch back to the old symbolic engine which finds the solution(s) with ease:

EDIT: I notice that I have a typo and the 5000 should be 5600
But it seems that you are just looking for a numeric result anyway, so why not use one of Primes numeric methods for solving an equation.
Either an ugly looking solve block or the "root" command in one of its two flavors:

BTW, a question to the community: Can anyone explain this error message which I get with a guess value larger than 0.5?

Looks like the algorithm tries values for x smaller than 10^-62, but why would he do so?