[NTG-context] t-tikz: problem with colorspace pgfprgb

Hi, I have the following problem with TikZ: When I use the "patterns" library in a tikzpicture environment, the file is compiled without problems and creates a PDF file. However, Acrobat displays an error message "Could not find the ColorSpace named 'pgfprgb'". So the patterns library seems to be a sufficient condition for this problem to occur. By contrast, the problem does not occur when I use pdflatex to create PDF from a LaTeX file with the same tikz-code. I have a standalone ConTeXt distribution and tikz 2.00, but I already had this problem with tikz 1.18. Any suggestions? Thanks, Finn Martensen