consecutive substitution failure

[halukhaluk]

Hi everyone,
I am having trouble with substiting a few large symbolic expressions. I have a number of similar vector elements to substitute, however, after calculating 2 or 3 of them (each at a time manually and in different orders), the next subs gives the error below. Has any one got an idea why this might happen?

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>> dQ2_subs=subs(dQ(2),q_sym,q_val)
??? Error using ==> maple
Error, (in evalm) evalm accepts only one argument, an expression

Error in ==> sym.subs at 229
NEWf = sym(maple('evalm',strrep(NEWf,'MATRIX','array')));
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Thanks a lot...
halukb