Sounds like you put a formation that doesn't conform to these rules on the pitch:

"Some formations are not allowed in Top Eleven and may lead to 20% ball possession, which in turn reduces the chance of victory.

Throughout the whole match you must have:

a goalkeeper (blue)
at least three defenders (green) (DL/DC/DR)
at least one striker (red)
at least one player on both flanks.
at least four players in the opponents half (ML/MC/MR or AML/AMC/AMR or ST)
at least three players in the midfield section (AML/AMC/AMR and/or ML/MC/MR and/or DML/DMC/DMR)

One player on each flank is enough, but three players on the same flank will also lead to 20% possession. "

From the wiki (wiki.topeleven.com)